Use of 3-aryl-4-isoxazolecarboxylic acid derivatives as herbicides

ABSTRACT

Carboxylic acid derivatives having the formula ##STR1## have been found to be effective herbicides. They are especially effective when applied as a pre-emergent herbicide.

This is a division, of application Ser. No. 852,164 filed Nov. 16, 1977 now U.S. Pat. No. 4,187,099.

The invention relates to the use of 3-aryl-4-isothiazolecarboxylic acid derivatives and 3-aryl-4-isoxazolecarboxylic acid derivatives as herbicides.

The carboxylates may be represented by the formula ##STR2## wherein E is oxygen or sulfur; X and Y are independently selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, trifluoromethyl, halogen, cyano and nitro; n is zero or one provided that when n is zero, Z is selected from the group consisting of chloro and NR₁ R₂ wherein R₁ and R₂ are independently selected from the group consisting of hydrogen and lower alkyl; when n is one, Z is selected from the group consisting of alkyl having up to 12 carbon atoms inclusive, haloalkyl, benzyl, lower alkoxy lower alkyl, allyl, monochlorinated allyl, dichlorinated allyl, ##STR3## and agriculturally acceptable cations; wherein R₁ and R₂ are as previously defined, R₃ is hydrogen or methyl and R₄ is lower alkyl.

As used herein, the term "lower alkyl" and "lower alkoxy" is understood to include those alkyl and alkoxy groups having up to 5 carbon atoms, inclusive. The term "haloalkyl" is understood to mean those lower alkyl groups which have been substituted with from 1 to 3 halogen atoms, inclusive. The term "argiculturally acceptable cations" is understood to mean those cations that are commonly used to form the salt of the free acid. Such cations include, but are not limited to, alkali metal, alkaline earth, substituted amine and ammonium cations. The term "alkyl" includes primary, secondary and tertiary alkyls.

The carboxylic acid derivatives of the foregoing formula have been found to be rather effective in inhibiting the growth of undesirable weeds, especially when applied in what is known in the art as a pre-emergent treatment. This is somewhat surprising in view of U.S. Pat. No. 3,403,209 wherein isothiazole carboxylates are disclosed to be fungicidal having very low phytotoxicity.

The compounds may be prepared utilizing a number of different procedures. The first procedure summarized below as Scheme A illustrates the preparation of 3-aryl-4-isothiazolecarboxylic acid esters. ##STR4##

In accordance with Scheme A, 1.25-1.50 equivalents of chlorocarbonylsulfonyl chloride prepared in accordance with British Pat. No. 1,079,348 is dissolved in a suitable solvent, such as toluene, along with the appropriate benzamide. The solution is stirred and heated at approximately 100° C. until gas evolution has nearly ceased and/or until an infrared spectrum has revealed the absence of residual amide. Up to 5.0 equivalents of chlorocarbonylsulfenyl chloride can be employed with less reactive amides. Concentration of the reaction mixture under vacuum and crystallization of the residue from an appropriate solvent results in a 5-aryl-1,3,4-oxathiazol-2-one.

A solution of 0.10 moles of the oxathiazolone and 0.20 moles of dimethyl acetylenedicarboxylate in 60 ml of an appropriate solvent, such as chlorobenzene, is stirred at reflux until CO₂ evolution ceases. After removal of the solvent and the excess dimethyl acetylenedicarboxylate, the dimethyl 4,5-isothiazoledicarboxylate is crystallized from an appropriate solvent.

The dicarboxylate is then hydrolyzed by first treating the dimethyl 4,5-isothiazoledicarboxylate with an excess of sodium hydroxide in water. For very insoluble esters, a small amount of dioxane may be added to the reaction mixture. The resultant solution may then be acidified to a pH of less than 1.0 with an excess of concentrated hydrochloric acid and then extracted several times with ether. The ether layers are combined, dried (CaSO₄), and concentrated under vacuum.

Monodecarboxylation of the 4,5-isothiazoledicarboxylic acids may then be effected by heating said acid in an appropriate solvent, such as o-dichlorobenzene at reflux. The solution is then allowed to cool and the solid product collected, washed and recrystallized.

Esters of the isothiazole-4-carboxylic acid may then be obtained by heating said acid with an excess of thionyl chloride at reflux. The resultant solution is concentrated under vacuum and heated at reflux with the appropriate alcohol. The solution may then be concentrated to give pure ester or in the case of solids, the solid may then be recrystallized.

In order to illustrate the preparation of 3-aryl-4-isothiazolecarboxylates by the methods of Scheme A, the following examples are presented.

All examples presented herein are only for purposes of illustration and are not intended as a limitation in the scope of the invention. All temperatures are understood to be Centigrade.

5-Aryl-1,3,4-oxathiazol-2-ones may be prepared in accordance with Examples 1-5.

EXAMPLE 1 Preparation of 5-Phenyl-1,3,4-Oxathiazol-2-One

Chlorocarbonylsulfenyl chloride was prepared by a literature procedure. A mixture of 784.9 g (4.22 mol) of trichloromethanesulfenyl chloride and 76 g (4.22 mol) of water dissolved in 886 ml of concentrated H₂ SO₄ was stirred at 45°-50° for 1 hour in a 5 l. flask, at which time the initially-copious HCl evolution had ceased. (Foaming presented problems in the beginning.) The mixture was transferred to a separately funnel, and after 15 minutes, the layers were separated. The top, fluid layer, which amounted to 404.3 (3.08 mol, 73% yield) of fairly pure chlorocarbonylsulfenyl chloride, was added to 373 g (3.08 mole) of benzamide in 1 l. of toluene in a 5 l. flask fitted with stirrer and reflux condenser. The mixture was stirred vigorously and was heated gently to 58°. A mildly exothermic reaction carried the temperature to 65° with foaming and vigorous gas evolution. The mixture was heated at 65°for 20 minutes, at 70° C. for 8 hours, at 70°-110° for 0.5 hours, and at 110° for 0.75 hours, at which time gas evolution had ceased. The reaction mixture was concentrated under vacuum to 1.5 mm and 90°. The residue was heated with 650 ml of methylcyclohexane; the mixture was treated with charcoal, filtered, and allowed to cool. The resultant solid was recrystallized from 650 ml of methylcyclohexane, heated to 75° (charcoal treatment and filtration) to give 375 g of very pale yellow solid, 5-phenyl-1,3,4-oxathiazol-2-one, m.p. 64°-67°. An additional 27.2 g of product, m.p. 64°-67°, was obtained from the filtrates. The total yield, 412.2 g, corresponds to 75% of the theoretical amount.

EXAMPLE 2 Preparation of 5-(m-Tolyl)-1,3,4-Oxathiazol-2-One

m-Toluamide (116 g, 0.86 mol) and chlorocarbonylsulfenyl chloride (144 g, 1.1 mol, 28% excess) was heated to 100° C. in 400 ml of toluene, with stirring, for 5.5 hours. Cooling resulted in an orange solid. The solid, isolated by filtration, was dissolved in hot methylcyclohexane and decolorized. The light yellow product was recrystallized once from methylcyclohexane to give 76.05 g (45.8%) of white solid, m.p. 82.5°-84°.

Anal. Calc'd. for C₉ H₇ NO₂ S: C, 55.94; H, 3.65. Found: C, 56.07; H, 3.59.

EXAMPLE 3 Preparation of 5-(m-Chlorophenyl)-1,3,4-Oxathiazol-2-One

m-Chlorobenzamide (75 g, 0.48 mol) and chlorocarbonylsulfenyl chloride (79 g, 0.6 mol, 25% excess) were reacted as described in Example 2 for 1.5 hours. Volatile components were removed under reduced pressure. The dark brown oil was taken up in hot cyclohexane, and the mixture was filtered. Cooling resulted in separation of a dark orange solid. The solid, recrystallized twice from hot ethyl acetate, gave 64.21 g (0.316 mol, 65.8%) of off-white solid, m.p. 83+-84.5°.

Anal. Calc'd. for C₈ H₄ ClNO₂ S: C, 44.97; H, 1.89. Found: C, 44.92; H, 1.62.

EXAMPLE 4 Preparation of 5-(α,α,α-Trifluoro-m-Tolyl)-1,3,4-Oxathiazol-2-One

α,α,α-Trifluoro-m-toluamide (82.7 g, 0.437 mol) and chlorocarbonylsulfenyl chloride (86 g, 0.667 mol, 53% excess) were reacted under the conditions of Example 2 for 0.5 hours. The light yellow residue was dissolved in ethyl acetate and cooled to -78°. The white precipitate was filtered and washed with hexane to yield 93.14 g (0.377 mol, 86.2%) of white solid, m.p. 85°-86.5°.

Anal. Calc'd. for C₉ H₄ F₃ NO₂ S: C, 4.373; H, 1.63. Found: C, 43.66; H, 1.58.

EXAMPLE 5 Preparation of 5-(α,α,α,α',α',α'-Hexafluoro-3,5-Xylyl)-1,3,4-Oxathiazol-2-One

3,5-Bis(trifluoromethyl)benzamide (60.5 g, 0.235 mol) and five equivalents of chlorocarbonylsulfenyl chloride (154 g, 1.175 mol) were heated in 600 ml of toluene at reflux, with stirring, for 12 hours. The crude product, a dark brown oil, weighed 77.5 g. After decolorization in hexane, the material was taken up in methanol and recrystallized three times to give 22.0 g (0.0699 mol, 29.75%) of pale gold solid, m.p. 61°-62.5°.

Anal. Calc'd. for C₁₀ H₃ F₆ NO₂ S: C, 38.11; H, 0.96. Found: C, 38.22; H, 0.90.

Additionally, the following compounds may be prepared in accordance with Examples 1-5.

5-(3',4'-dimethoxyphenyl)-1,3,4-oxathiazol-2-one, m.p. 143°-144.5°.

5-(3',4'-dichlorophenyl)-1,3,4-oxathiazol-2-one, m.p. 130.5°-131.5°.

5-(p-cyanophenyl)-1,3,4-oxathiazol-2-one, m.p. 173° with decomposition.

5-(p-nitrophenyl)-1,3,4-oxathiazol-2-one, m.p. 168°-169° with decomposition.

5-(p-chlorophenyl-1,3,4-oxathiazol-2-one, m.p. 129°-131°.

5-(m-nitrophenyl)-1,3,4-oxathiazol-2-one, m.p. 95°-96.5°.

The dicarboxylate may be prepared in accordance with Examples 6-13.

EXAMPLE 6 Preparation of Dimethyl 3-Phenyl-4,5-Isothiazoledicarboxylate

A solution of 412.2 g (2.3 mol) of 5-phenyl-1,3,4-oxathiazol-2-one, 662.7 g (4.66 mol) of dimethyl acetylenedicarboxylate, and 1 l. of chlorobenzene was heated at 135° for 6.5 hours, at which time CO₂ evolution became very slow. Infrared and gas chromatography assays also indicated that the reaction was complete. The reaction mixture was concentrated under vacuum to 0.2 mm and 90°. The 680 g of pot residue was crystallized from about 700 ml of methanol to give 393 g of solid dimethyl 3-phenyl-4,5-isothiazoledicarboxylate, m.p. 70°-71.5°. An additional 69.9 g of solid, m.p. 70°-72°, was obtained from the filtrate. The total of 462.9 g mounted to a 72.7% yield.

EXAMPLE 7 Preparation of Dimethyl 3-(α,α,α,α',α',α'- Hexafluoro-3,5-Xylyl)-4,5-Isothiazoledicarboxylate

A solution of 20.7 g (0.0657 mol) of 5-(α,α,α,α',α',α'-hexafluoro-3,5-xylyl)-1,3,4-oxathiazol-2-one and 18.7 g (0.131 mol) of dimethyl acetylenedicarboxylate in 52 g of o-dichlorobenzene was held at reflux for 10 hours (gas chromatography assay revealed the product had formed in 77% yield) and was concentrated under vacuum to 90° at 0.5 torr. The residue was crystallized from methanol to give 17.9 g of solid, m.p. 71°-74°. The solid was recrystallized to give 14.3 g (53% yield) of white solid, m.p. 73°-75°.

Anal. Calc'd. for C₁₅ H₉ F₆ NO₄ S: C, 43.59; H, 2.19. Found: C, 43.77; H, 2.13.

EXAMPLE 8 Preparation of Dimethyl 3-(3,4-Dimethoxyphenyl)-4,5-Isothiazoledicarboxylate

5-(3,4-Dimethoxyphenyl)-1,3,4-oxathiazol-2-one (58 g, 0.24 mol) and dimethyl acetylenedicarboxylate (70 g, 0.49 mol) were heated at reflux in 120 ml of chlorobenzene for 43 hours. The residue crystallized from methanol at -29°, was recrystallized once from methanol, twice from ethyl acetate, and twice from methylcyclohexane to yield 59.07 g (0.175 mol, 73.0%) of pale yellow solid, m.p. 113.5°-11.45°.

Anal. Calc'd. for C₁₅ H_(NO) ₆ S: C, 53.41; H, 4.48. Found: C, 53.03; H, 4.46.

EXAMPLE 9 Preparation of Dimethyl 3-(3,4-Dichlorophenyl)-4,5-Tsothiazoledicarboxylate

5-(3,4-Dichlorophenyl)-1,3,4-oxathiazol-2-one (99.2 g, 0.4 mol) and dimethyl acetylenedicarboxylate (113.5 g, 0.8 mol) were heated in 240 ml of chlorobenzene at reflux for 47 hours. The product, from hot methanol, was recrystallized twice from hot methanol to give 97.8 g (0.283 mol, 70.7%) of white solid, m.p. 105°-107°.

Anal. Calc'd. for C₁₃ H₉ Cl₂ NO₄ S: C, 45.10; H, 2.62. Found: C, 45.12; H, 2.58.

EXAMPLE 10 Preparation of Dimethyl 3-(p-Cyanophenyl)-4,5-Isothiazoledicarboxylate

Dimethyl acetylenedicarboxylate (42.63 g, 0.4 mol) and 5-(p-cyanophenyl)-1,3,4-oxathiazol-2-one (20.42 g, 0.1 mol) were heated at reflux in o-dichlorobenzene for 10 hours. Volatile materials were removed under reduced pressure (1 mm). The red-brown residue contained at least three contaminants (g.c.) which were removed by crystallization from methanol. Four recrystallizations resulted in 18.1 g (0.0598 mol, 59.8%) of light yellow solid, m.p. 134°-135°.

Anal. Calc'd. for C₁₄ H₁₀ N₂ O_(S:) C, 55.62; H, 3.33. Found: C, 55.55; H, 3.23.

EXAMPLE 11 Preparation of Dimethyl 3-(p-Nitrophenyl)-4,5-Isothiazoledicarboxylate

Dimethyl acetylenedicarboxylate (85.26 g, 0.6 mol) and 5-(p-nitrophenyl)-1,3,4-oxathiazol-2-one (33.63 g, 0.15 mol) were heated as given above for 15 hours. Crystallization of the brown solid from methanol (2×) gave little improvement in purity. The brown solid was decolorized in ethyl acetate solution and recrystallized (3×) to give 12.2 g (0.0378 mol, 25.2%) of dark gold solid, m.p. 142°-143°.

Anal. Calc'd. for C₁₃ H₁₀ N₂ O₆ S: C, 48.45; H, 3.13. Found: C, 48.76; H, 3.18.

EXAMPLE 12 Preparation of Dimethyl 3-(m-Tolyl)-4,5-Isothiazoledicarboxylate

5-m-Tolyl-1,3,4-oxathiazol-2-one (19.32 g, 0.1 mol) and dimethyl acetylenedicarboxylate (28.42 g, 0.2 mol) were heated at reflux in 60 ml of chlorobenzene as given above. After the initial crystallization from cold methanol, three recrystallizations from diethyl ether/petroleum ether gave 15.18 g (0.0522 mol, 52.2%) of white solid, m.p. 53°-54.5°.

Anal. Calc'd. for C₁₄ H₁₃ NO₄ S: C, 57.72; H, 4.50. Found: C, 57.79; H, 4.20.

EXAMPLE 13 Preparation of Dimethyl 3-(m-Chlorophenyl)-4,5-Isothiazoledicarboxylate

5-(m-Chlorophenyl)-1,3,4-oxathiazol-2-one (21.37 g, 0.1 mol) and dimethyl acetylenedicarboxylate (28.42 g, 0.2 mol) were heated in 60 ml of chlorobenzene at reflux as above for 32 hours. After crystallization once from methanol and twice from diethyl ether/petroleum ether, 16.11 g (0.0517 mol, 51.7%) of pale yellow solid was obtained, m.p. 69°-70°.

Anal. Calc'd. for C₁₃ H₁₀ ClNO₄ S: C, 50.09; H, 3.23. Found: C, 50.24; H, 3.42.

Hydrolysis of the dicarboxylate is illustrated by Examples 14-19.

EXAMPLE 14 Preparation of 3-(α,α,α,α',α',α'-Hexafluoro-3,5-Xylyl)-4,5-Isothiazoledicarboxylic Acid

A mixture of 14.7 g (0.0356 mol) of dimethyl 3-(α,α,α,α',α',α'-hexafluoro-3,5-xylyl)-4,5-isothiazoledicarboxylate, 7.2 g (0.18 mol) of NaOH, and 45 ml of water was held at reflux for 2 hours, was cooled, extracted twice with ether, and acidified with 30 ml (0.36 mol) of concentrated HCl. The resultant mixture was extracted three times with ether; these ether extracts were combined, dried (CaSO₄), and concentrated under vacuum to 12.8 g (93.4%) of white solid, m.p. 193°-193.5° with decomposition.

Anal. Calc'd. for C₁₃ H₅ F₆ NO₄ S: C, 40.53; H, 1.31. Found: C, 40.31; H, 1.18.

EXAMPLE 15 Preparation of 3-(3,4-Dimethoxyphenyl)-4,5-Isothiazoledicarboxylic Acid

The diester was hydrolyzed with five equivalents of NaOH in aqueous dioxane at reflux for 3 hours. The mixture was cooled, acidified with concentrated HCl, and extracted several times with ether (total volume=3 l.) and with 1.5 l. of 1:1 ether-THF. The organic layers were combined, dried (CaSO₄), and concentrated to give 45.06 g of crude product. A sample was recrystallized twice from 90% aqueous ethanol to give a hydrated product, m.p. 190.5°-191.5° with decomposition (fast), m.p. 216°-217° with decomposition (slow; monoacid).

Anal. Calc'd. for C₁₃ H₁₁ NO₆ S.0.7 H₂ O: C, 48.50; H, 3.88. Found: C, 48.73; H, 4.10.

EXAMPLE 16 Preparation of 3-(3,4-Dichlorophenyl)-4,5-Isothiazoledicarboxylic Acid

A mixture of 51.9 g (0.15 mol) of dimethyl 3-(3,4-dichlorophenyl)-4,5-isothiazoledicarboxylate and 30 g (0.75 mol) of NaOH in 150 ml of water was held at reflux for 2 hours, was cooled, acidified with HCl, and was extracted with ether several times (total ether volume equals 1300 ml). The ether solution was dried (CaSO₄) and concentrated to give 46.12 g of solid. A small sample was recrystallized twice from water and once from ether-dichloroethane to give pure product, m.p. 187.5°-188.5° with decomposition (fast).

Anal. Calc'd. for C₁₁ H₅ Cl₂ NO₄ S: C, 41.53; H, 1.58. Found: C, 41.56; H, 1.60.

EXAMPLE 17 Preparation of 3-(m-Tolyl)-4,5-Isothiazoledicarboxylic Acid

Dimethyl 3-(m-tolyl)-4,5-isothiazoledicarboxylate (14.03 g, 0.0548 mol) was hydrolyzed in NaOH (10.96 g, 0.274 mol) and 50 ml H₂ O for 0.5 hours at reflux. Acidification with HCl, extraction with ether and recrystallization gave a light yellow solid, m.p. 166.5°-167° with decomposition.

Anal. Calc'd. for C₁₂ H₉ NO₄ S: C, 54.75; H, 3.45. Found: C, 54.54; H, 3.63.

EXAMPLE 18 Preparation of 3-(m-Chlorophenyl)-4,5-Isothiazoledicarboxylic Acid

Dimethyl 3-(m-chlorophenyl)-4,5-isothiazoledicarboxylate (14.51 g, 0.0504 mol) was hydrolyzed as given above with NaOH (10.08 g, 0.252 mol) and then acidified with HCl. The purified yellow solid had m.p. 185°-6° with decomposition (rapid heating of the sample produced normal decomposition in this temperature range; slow heating caused a color change to red and m.p. 217.5°-218.5° with decomposition. Infrared of material heated slowly to 190° showed that it was 3-(m-chlorophenyl)-4-isothiazolecarboxylic acid).

Anal. Calc'd. for C₁₁ H₆ ClNO₄ S: C, 46.57; H, 2.13. Found: C, 46.50; H, 2.17.

EXAMPLE 19 Preparation of 3-(p-Chlorophenyl)-4,5-Isothiazoledicarboxylic Acid

Dimethyl 3-(p-chlorophenyl)-4,5-isothiazoledicarboxylate (35.0 g, 0.112 mol) was hydrolyzed in NaOH (22.6 g, 0.56 mol) as stated above. Acidification with HCl and the usual workup as in Example 14 gave a purified pale yellow solid which had m.p. 177°-177.5° with decomposition.

Anal. Calc'd. for C₁₁ H₆ ClNO₄ S: C, 46.57; H, 2.13. Found: C, 46.22; H, 2.26.

Decarboxylation of the dicarboxylic acids is illustrated by Examples 20-25.

EXAMPLE 20 Preparation of 3-(m-Tolyl)-4-Isothiazolecarboxylic Acid

3-(m-Tolyl)-4,5-isothiazoledicarboxylic acid (7.98 g, 0.0303 mol) was heated in 25 ml of o-dichlorobenzene at vigorous reflux for 15 minutes and cooled. Hexane was added and the resultant precipitate was filtered off to yield 5.52 g (0.0258 mol, 83.1%) of a light pink solid, m.p. 144.5°-146°.

Anal. Calc'd. for C₁₁ H₉ NO₂ S: C, 60.26; H, 4.14. Found: C, 60.21; H, 4.04.

EXAMPLE 21 Preparation of 3-(m-Chlorophenyl)-4-Isothiazolecarboxylic Acid

3-(m-Chlorophenyl)-4,5-isothiazoledicarboxylic acid (8.0 g, 0.0282 mol) was reacted as previously stated. The dark tan solid was crystallized from ethylene chloride/acetonitrile solution to give 5.84 g (0.0244 mol, 86.6%) of white solid, m.p. 215°-216°.

Anal. Calc'd. for C₁₀ H₆ ClNO₂ S: C, 50.11; H, 2.52. Found: C, 50.32; H, 2.47.

EXAMPLE 22 Preparation of 3-(p-Chlorophenyl)-4-Isothiazolecarboxylic Acid

3-(p-Chlorophenyl)-4,5-isothiazoledicarboxylic acid recrystallization residues were heated at reflux as given above for 0.5 hours. On cooling a tan precipitate formed which was crystallized from acetonitrile and from ethylene chloride to yield a white solid having m.p. 181.5°-182.5°.

EXAMPLE 23 Preparation of 3-(α,α,α,α',α',α'-Hexafluoro-3,5-Xylyl)-4-Isothiazolecarboxylic Acid

A solution of 11.7 g of diacid in 100 ml of o-dichlorobenzene and 30 ml of ether was heated on a hot plate, and the ether was allowed to distill off. The solution was allowed to boil at 180° for 10 minutes, was cooled, and was filtered to give a solid. This material was recrystallized from heptane to give 5.52 g of white solid, m.p. 152°-154°.

Anal. Calc'd. for C₁₂ H₅ F₆ NO₂ S: C, 42.24; H, 1.48. Found: C, 42.13; H, 1.34.

An additional 3.14 g of solid, m.p. 151°-153.5° was obtained by concentration of the o-dichlorobenzene filtrate and crystallization of the residue once from heptane and once from 1,2-dichloroethane.

EXAMPLE 24 Preparation of 3-(3,4-Dimethoxyphenyl)-4-Isothiazolecarboxylic Acid

A 42 g sample of diacid was heated in 100 ml of nitrobenzene at reflux for 15 minutes. The solution was cooled, diluted with 150 ml of hexane, and filtered. The resultant solid was crystallized twice from dioxane and once from 85% aqueous ethanol to give 32.6 g (90%) of solid, m.p. 215.5°-216° with decomposition.

Anal. Calc'd. for C₁₂ H₁₁ NO₄ S.0.2 H₂ O: C, 53.60; H, 4.27. Found: C, 53.63; H, 4.20.

A small sample was recrystallized twice from ethyl acetate and dried at 80° (<0.1 torr).

Anal. Calc'd. for C₁₂ H₁₁ NO₄ S: C, 54.33; H, 4.18. Found: C, 54.32; H, 4.24.

EXAMPLE 25 Preparation of 3-(3,4-Dichlorophenyl)-4-Isothiazolecarboxylic Acid

A 19.1 g sample of diacid was heated in o-dichlorobenzene at reflux for 15 minutes. Cyclohexane was added to the cooled mixture, and the resultant 14.41 g of solid was recrystallized from 90% aqueous ethanol and from ethertoluene to give pure product, m.p. 247°-247.5° with decomposition.

Anal. Calc'd. for C₁₀ H₅ Cl₂ NO₂ S: C, 43.82; H, 1.84. Found: C, 43.84; H, 1.87.

Examples 26-45 illustrate the esterification of 3-aryl-4-isothiazolecarboxylic acid by preparing the acid chloride with thionyl chloride and reacting said acid chloride with the appropriate alcohol.

EXAMPLE 26 Preparation of Methyl 3-(α,α,α,α',α',α'-Hexafluoro-3,5-Xylyl)-4-Isothiazolecarboxylate

A solution of 7.50 g (0.022 mole) of 3-(α,α,α,α',α',α'-hexafluoro-3,5-xylyl)-4-isothiazolecarboxylic acid and 20 ml (32.8 g, 0.276 mol) of thionyl chloride was held at reflux on a steam bath for 0.5 hours and was concentrated under vacuum to 7.6 g of acid chloride, an oil.

A solution of 2.50 g of acid chloride and 10 ml of methanol was held at reflux for 0.5 hours, filtered, and concentrated to 90° (0.4 torr) to 2.23 g (90% yield) of oil, n_(D) ²³ =1.4966, that slowly crystallized, m.p. 45°-46.5°.

Anal. Calc'd. for C₁₃ H₇ F₆ NO₂ S: C, 43.95; H, 1.99. Found: C, 44.12; H, 2.14.

EXAMPLE 27 Preparation of Ethyl 3-(α,α,α,α',α',α'-Hexafluoro-3,5-Xylyl)-4-Isothiazolecarboxylate

Use of a similar procedure to that above gave the product in 96% yield as an oil, n_(D) ²³ =1.4901, that slowly crystallized, m.p. 61.5°-63°.

Anal. Calc'd. for C₁₄ H₉ F₆ NO₂ S: C, 45.53; H, 2.46. Found: C, 45.31; H, 2.51.

EXAMPLE 28

Preparation of Propyl 3-(α,α,α,α',α',α'-Hexafluoro-3,5-Xylyl)-4-Isothiazolecarboxylate

A solution of 2.50 g of acid chloride and 10 ml of 1-propanol was heated on a steam bath for 2 hours, filtered, and concentrated under vacuum to 90° (0.4 torr) to give 2.52 g (94% yield) of oil, n_(D) ²³ =1.4875.

Anal. Calc'd. for C₁₅ H₁₁ F₆ NO₂ S: C, 47.00; H, 2.89. Found: C, 47.01; H, 2.86.

EXAMPLE 29 Preparation of Ethyl 3-(3,4-Dimethoxyphenyl)-4-Isothiazolecarboxylate

A solution of 29.7 g (0.112 mol) of acid and 70.3 g (5 equivalents) of thionyl chloride was heated on a steam bath for 0.75 hours, concentrated under vacuum, heated in 50 ml of ethanol at reflux for 45 minutes, concentrated under vacuum, and the residue was crystallized from ethanol-hexane to give 32.05 g (98%) of solid, m.p. 74°-75.5°.

Anal. Calc'd. for C₁₄ H₁₅ NO₄ S: C, 57.32; H, 5.15. Found: C, 57.36; H, 5.14.

EXAMPLE 30 Preparation of Methyl 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylate

A solution of 2.92 g (0.010 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride prepared as in Example 29 and 10 ml of methanol was held at reflux for 0.5 hours and was concentrated under vacuum to 80° (0.3 torr) to 2.72 g of oil, n_(D) ²³.4° =1.5404.

Anal. Calc'd. for C₁₂ H₈ F₃ NO₂ S: C, 50.17; H, 2.81. Found: C, 50.26; H, 2.88.

EXAMPLE 31 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Isopropyl Ester

A solution of 2.92 g (0.010 mol) of acid chloride prepared as in Example 29 and 10 ml of isopropyl alcohol was heated on a steam bath for 1.5 hours, filtered, and concentrated under vacuum to 90° (0.2 torr) to give 2.95 g of colorless oil, n_(D) ²⁴ =1.5225.

Anal. Calc'd. for C₁₄ H₁₂ F₃ NO₂ S: C, 53.33; H, 3.84. Found: C, 53.16; H, 3.77.

EXAMPLE 32 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2,2,2-Trifluoroethyl Ester

A solution of 2.50 g (0.00856 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride and 50 ml of 2,2,2-trifluoroethanol was held at reflux for 40 minutes, was allowed to stand overnight, and was concentrated under vacuum (to 90° at 0.1 torr) to give 2.68 g (88%) of oil, n_(D) ²⁴ =1.4976.

Anal. Calc'd. for C₁₃ H₇ F₆ NO₂ S: C, 43.95; H, 1.99. Found: C, 43.73; H, 1.98.

EXAMPLE 33 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2,2,2-Trichloroethyl Ester

A solution of 2.0 g (0.0069 mol) of 3-(α,α,α-trifluoro-m-tolyl-4-isothiazolecarbonyl chloride and 1.22 g (1.18 equivalents) of 2,2,2-trichloroethanol was heated at 70°-140° in an oil bath for 6.5 hours. The reaction mixture was concentrated under vacuum to give 1.78 g of oil, n_(D) ²³ =1.5499 (yield 63.8%).

Anal. Calc'd. for C₁₃ H₇ Cl₃ F₃ NO₂ S: C, 38.59; H, 1.74; N, 3.46. Found: C, 38.28; H, 1.69; N, 3.19.

EXAMPLE 34 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2-Chloroethyl Ester

By a procedure similar to that used for Example 33, there was obtained 1.65 g of oil, n_(D) ²³ =1.5452 (yield 72%).

Anal. Calc'd. for C₁₃ H₉ ClF₃ NO₂ S: C, 46.51; H, 2.70; N, 4.17. Found: C, 46.54; H, 2.55; N, 4.10.

EXAMPLE 35 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, n-Octyl Ester

A solution of 1.0 g (0.0034 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride and 0.45 g (1 equivalent) of 1-octanol was heated on a steam bath for 2.0 hours. The reaction mixture was dissolved in ether, dried, filtered, and concentrated under vacuum to give 1.04 g of oil, n_(D) ²³.2 =1.5107 (yield 78.7%).

Anal. Calc'd. for C₁₉ H₂₂ F₃ NO₂ S: C, 59.21; H, 5.75; N, 3.63. Found: C, 59.06; H, 5.60; N, 3.63.

EXAMPLE 36 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, n-Hexyl Ester

By a procedure similar to that used for Example 35, using excess n-hexanol, there was obtained 0.91 g of oil, n_(D) ²³ =1.5094 (yield 74.9%).

Anal. Calc'd. for C₁₇ H₁₈ F₃ NO₂ S: C, 57.13; H, 5.08; N, 3.92. Found: C, 57.67; H, 5.15; N, 3.68.

EXAMPLE 37 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl-4-Isothiazolecarboxylic Acid, Allyl Ester

By a procedure similar to that used for Example 35, using excess alcohol, there was obtained 0.55 g of oil, n_(D) ²³ =1.5360 (yield 51.6%).

Anal. Calc'd. for C₁₄ H₁₀ F₃ NO₂ S: C, 53.67; H, 3.22; N, 4.47. Found: C, 54.00; H, 3.56; N, 4.70.

EXAMPLE 38 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2-Chloroallyl Ester By a procedure similar to that used for Example 33, there was obtained 0.65 g of an oil, n_(D) ²³.2 =1.5468 (yield 55%).

Anal. Calc'd. for C₁₄ H₉ ClF₃ NO₂ S: C, 48.36; H, 2.61; N, 4.03. Found: C, 48.26; H, 2.69; N, 4.06.

EXAMPLE 39 Preparation of 3-(m-Nitrophenyl)-4-Isothiazolecarboxylic Acid, Ethyl Ester

A solution of 1.5 (0.006 mol) of the free acid prepared in accordance with Scheme A and excess thionyl chloride was heated on a steam bath for 0.75 hours. The reaction mixture was concentrated under vacuum. A solution of the residue and 15 cc of ethanol was heated on a steam bath for 0.75 hours and cooled to give a solid. The solid was recrystallized twice from ethanol to give 1.0 g solid, m.p. 136.5°-138°. The first filtrate residue was crystallized from ethanol to give 0.2 g solid, m.p. 132°-136°. (Total yield 71.9%).

Anal. Calc'd. for C₁₂ H₁₀ N₂ O₄ S: C, 51.79; H, 3.62; N, 10.07. Found: C, 51.85; H, 3.38; N, 10.07.

EXAMPLE 40 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Propyl Ester

A solution of 2.92 g (0.010 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride and 4 g (0.0667 mol) of 1-propanol was heated on a steam bath for 1 hour and was concentrated under vacuum to 70° (0.5 torr) to give 3.17 g of clear oil, n_(D) ²⁰.8 =1.5261, infrared (film) 5.80μ.

Anal. Calc'd. for C₁₄ H₁₂ F₃ NO₂ S: C, 53.33; N, 3.84. Found: C, 53.67; H, 4.01.

EXAMPLE 41 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Butyl Ester

A solution of 2.92 g (0.010 mol) of acid chloride and 0.80 g (0.0108 mol) of 1-butanol was heated in an oil bath at 110° for 2 hours and was concentrated under vacuum to 90° (0.4 Torr) to give 3.01 g (91%) of oil, n_(D) ²⁰.5 =1.5221, infrared (film) 5.80μ.

Anal. Calc'd. for C₁₅ H₁₄ F₃ NO₂ S: C, 54.70; H, 4.28. Found: C, 54.46; H, 4.09.

EXAMPLE 42 Preparation of 3-(α,α,α-Trifluoromethyl-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2-Butoxyethyl Ester

A solution of 2.92 g (0.010 mol) of acid chloride and 1.22 g (0.0103 mol) of 2-butoxyethanol was heated in an oil bath at 110°-115° for 3 hours and was concentrated under vacuum to 90° (0.04 torr) to 3.66 g of oil, n_(D) ²².4 =1.5152, infrared (film) 5.80μ.

Anal. Calc'd. for C₁₇ H₁₈ F₃ NO₃ S: C, 54.68; H, 4.86. Found: C, 54.67; H, 4.80.

EXAMPLE 43 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, m-Cumenyl Ester

A solution of 2.92 g (0.010 mol) of acid chloride and 1.36 g (0.010 mol) of pure m-isopropylphenol was heated in an oil bath at 115°-120° for 2 hours and was concentrated under vacuum at 90° (0.6 torr) to 3.90 g (100%) of oil, n_(D) ²¹ =1.5611, infrared (film) 5.74μ.

Anal. Calc'd. for C₂₀ H₁₆ F₃ NO₂ S: C, 61.37; H, 4.12. Found: C, 61.22; H, 3.97.

EXAMPLE 44 Preparation of 3-(m-Chlorophenyl)-4-Isothiazolecarboxylic Acid, Ethyl Ester

Utilizing a procedure similar to Example 39, there was obtained a solid, m.p. 66.5°-68°.

Anal. Calc'd. for C₁₂ H₁₀ ClNO₂ S: C, 53.83; H, 3.76. Found: C, 53.86; H, 3.73.

EXAMPLE 45 Preparation of 3-(3',4'-Dichlorophenyl)-4-Isothiazolecarboxylic Acid, Ethyl Ester

Utilizing the procedure of Example 39, there was obtained a solid, m.p. 111.5°-112°.

Anal. Calc'd. for C₁₂ H₉ Cl₂ NO₂ S: C, 47.70; H, 3.00. Found: C, 47.61; H, 3.02.

The 3-aryl-4-isothiazolecarboxylates of the invention may also be prepared by adding aryl Grignard reagents to alkyl cyanoacetate. The resultant β-aminocinnamates are converted to the carboxylate via a Vilsmeier-Haack reaction, thiation and oxidation. For purposes of clarity, Scheme B is provided below. ##STR5##

In accordance with Scheme B, 1.0 mole of alkyl cyanoacetate is treated with two moles of aryl magnesium bromide in ether while stirring at temperatures from -75° to room temperature. The mixture is then heated at reflux until gas chromatographic analysis of hydrolyzed aliquots of the reaction mixture revealed the reaction to be complete. Then, the reaction mixture is cooled to about 10° or below and poured slowly into a 1.7 liter mixture of ice-water containing 2.0 moles of NH₄ Cl. This mixture is shaken with an ice-cold solution of 2.0 moles of HCl in 500 ml of water. The layers are separated and the aqueous layer is then extracted with ether. The ether layers are combined, dried (CaSO₄), and concentrated under vacuum to give crude alkyl β-aminocinnamate.

To a solution of 0.10 moles of the appropriate alkyl β-aminocinnamate in 90 ml of dimethylformamide is added 0.10 moles of phosphorous oxychloride while stirring at -60° under dry N₂. After warming to about 15°-25°, the mixture is stirred at about 25° for about ten minutes. The solution is then poured into an ice-cold solution of 0.11 moles of Na₂ S.9H₂ O in 110 ml of water. The resultant mixture is stirred for about five minutes and extracted with benzene. The benzene layers are dried (CaSO₄) and then 0.1 moles of I₂ in 200 ml of benzene is then added at 20°-30°. The dark benzene solution is then washed with an aqueous K₂ CO₃ solution and an aqueous solution of Na₂ S₂ O₃. A third washing with an aqueous K₂ CO₃ solution, drying (CaSO₄) and concentration under vacuum gives the crude isothiazolecarboxylate.

In order to illustrate the preparation of the 3-aryl-4-isothiazolecarboxylates by the methods of Scheme B, the following examples are presented.

The preparation of β-aminocinnamates is illustrated by Examples 46-50.

EXAMPLE 46 Preparation of Ethyl β-Aminocinnamate

Bromobenzene (235 g, 1.5 mol) in 200 ml of anhydrous ether was added dropwise, with stirring, to 36.5 g of magnesium turnings (1.5 mol) in about 400 ml of ether according to literature methods. When addition was complete, the mixture was heated at reflux for one hour and then cooled to <20°. To the cooled Grignard reagent was added dropwise, with stirring, 0.5 equivalents of ethyl cyanoacetate (84.9 g, 0.75 mol). The temperature was kept below 20° by cooling in ice. During the addition, the formation of a gelatinous solid was noted. On completion of addition of the ester, a 2-ml aliquot of the reaction mixture was hydrolyzed with saturated NH₄ Cl; gas chromatography of the ether layer showed that some product was already present. The reaction mixture was heated to reflux for 19 hours. Hydrolysis of the mixture with 1500 ml of ice-cold saturated NH₄ Cl was exothermic. Extraction of this mixture with ether proved very difficult due to the presence of a persistent gummy emulsion, until it was determined that addition of 2 N HCl to just the emulsion in the separatory funnel, only to the point of separation into 2 neat layers, would result in a pH decrease to about 7-7.5 without destroying the desired product. The ether extracts were dried (CaSO₄) and concentrated under reduced pressure to yield 127.7 g of gold-yellow residue, which was vacuum distilled twice to give 86.01 g (60% yield by weight) of pure material, boiling point 110°-112° (0.2 mm).

EXAMPLE 47 Preparation of Ethyl β-Amino-m-Trifluoromethylcinnamate

Phenylmagnesium bromide was prepared from 70 g (0.445 mol) of bromobenzene and 11.1 g (0.458 mol) of magnesium in 300 ml of ether. Then, 50.3 g (0.445 mol) of ethyl cyanoacetate was added dropwise with stirring at -55° to -35° (vigorous exothermic reaction after about 20-30% of the ethyl cyanoacetate added, even with Dry ice-acetone bath cooling). A very heavy precipitate formed that prevented stirring. The mixture was allowed to warm to 15°.

A solution of m-(trifluoromethyl)phenylmagnesium bromide, prepared from 100 g (0.445 mol) of m-bromobenzotrifluoride and 11.1 g (0.458 mol) of magnesium, in 300 ml of ether was added to the above mixture. The resultant mixture was stirred at reflux for 44 hours and then was cooled. A solution of 53 g (1.0 mol) of NH₄ Cl in 300 ml of water was added slowly with stirring at 10°-20°, and then 0.90 mol of 2 N HCl was slowly added. The layers were shaken together in a separatory funnel and were separated. The aqueous layer was extracted with two 250-ml portions of ether. The ether layers were combined, dried (CaSO₄), and concentrated under vacuum to 95.7 g of black oil. Gas chromatography assay of this oil on a 10 ft. 5% SE-30 column at 220° showed there was less than 1% (none detected) of ethyl β-aminocinnamate in the ethyl β-amino-m-trifluoromethylcinnamate, which elutes first. Gas chromatography assay of a weighed aliquot of the oil with a weighed quantity of o-dichlorobenzene and use of a calibration mixture revealed that the 95.7 g of oil contained 74.8% product (62% yield). Distillation of the oil gave 72.9 g of 94% pure product (60% yield), boiling point 110°-115° (0.05 torr). Redistillation of a small amount of this material gave a 99-100% pure sample, boiling point 106°-107° (0.06 torr).

Anal. Calc'd. for C₁₂ H₁₂ F₃ NO₂ : C, 55.60; H, 4.67. Found: C, 55.42; H, 4.36.

EXAMPLE 48 Preparation of Ethyl β-Amino-p-Trifluoromethylcinnamate

To the Grignard reagent prepared from 98 g (0.436 mol) of p-bromobenzotrifluoride and 10.59 g (0.436 mol) of magnesium in ether was added 24.65 g (0.218 mol) of ethyl cyanoacetate dropwise with stirring and cooling in an ice bath. The resultant mixture was stirred at reflux for 24 hours. The usual workup gave 49.4 g of dark red-brown residue; distillation of this material gave 16.73 g (30%) of product, boiling point 120°-123° (0.15 torr).

Anal. Calc'd. for C₁₂ H₁₂ F₃ NO₃ : C, 55.60; H, 4.67. Found: C, 56.67; H, 4.63.

EXAMPLE 49 Preparation of Ethyl β-Amino-m-Methylcinnamate

To 202 ml of 2.9 M phenylmagnesium bromide in ether (0.585 mol) was added 100 ml of ether. Then, 66.1 g (0.585 mol) of ethyl cyanoacetate was added over a few minutes with stirring at -40° to -15°. A heavy, thick precipitate formed that made stirring difficult. The mixture was allowed to warm slowly to 20°. Then, the Grignard reagent prepared from 100 g (0.585 mol) of 3-bromotoluene and 14.4 g (0.593 mol) of magnesium turnings in 300 ml of ether was added. The mixture was stirred at reflux for 4 hours, cooled, and poured slowly with stirring into 1 l. of ice-water mixture in which 62.6 g (1.17 mol) of NH₄ Cl was dissolved. Then, an ice-cold solution of 1.17 mol of HCl in 300 ml of water was added with stirring. The two layers were shaken together and separated. The aqueous layer was extracted with two 200-ml portions of ether. The ether layers were combined, dried (CaSO₄), and concentrated under aspirator vacuum to 112.0 g of oil that contained 78.4 g (65% yield) of product (gas chromatography assay with internal standard). The oil was distilled to give 83.2 g of 89% pure product (62% yield of ester), boiling point 120°-130° (0.08 torr). Redistillation of the product through a fractionating column gave 57.2 g (48%) of 97% pure product, boiling point 118° (0.05 torr). A small sample was redistilled to give 100% pure material, boiling point 118° (0.1 torr).

Anal. Calc'd. for C₁₂ H₁₅ NO₂ : C, 70.22; H, 7.37. Found: C, 70.31; H, 7.44.

EXAMPLE 50 Preparation of Ethyl β-Amino-m-Isopropylcinnamate

To the Grignard reagent prepared from 39.5 g (0.198 mol) of m-bromocumene and 4.9 g (0.20 mol) of magnesium in 150 ml of ether was added 11.2 g (0.099 mol) of ethyl cyanoacetate dropwise with stirring at 10°. The mixture was stirred at reflux for 22 hours and was allowed to stand at 23° for four days. Then, 10.6 g (0.20 mol) of NH₄ Cl in 60 ml of water was added with stirring at 10°-15°, followed by 0.20 mol of 2 N HCl at 0°. The layers were separated, and the water layer was extracted with 100 ml of ether. The ether layers was combined, extracted with dilute NaHCO₃ solution, dried (CaSO₄), and distilled to give 4.95 g of 80% pure product, boiling point 139°-142° (0.15 torr) and 0.87 g of about 97% pure product, boiling point 142°-143° (0.15 torr). [Infrared analysis of the lower-boiling impurity indicated it to be bi(m-cumenyl)].

Anal. Calc'd. for 97% C₁₄ H₁₉ NO₂ -3% C₁₈ H₂₂ : C, 72.60; H, 8.24; N, 5.82. Found: C, 72.60; H, 8.46; N, 5.84.

Preparation of 3-aryl-4-isothiazolecarboxylates from the β-aminocinnamates is illustrated by Examples 51-55.

EXAMPLE 51 Preparation of Ethyl 3-Phenyl-4-Isothiazolecarboxylate

1.91 g of ethyl β-aminocinnamate (0.01 mol) and 6 ml of dimethyl formamide 5.68 g, 0.073 mol) were cooled to -60°, with stirring. Then 1.533 g (0.917 ml, 0.01 mol) of POCl₃ was added and the mixture allowed to warm up exothermically to about 25°. It was then poured into an ice-cold solution of 2.40 g Na₂ S nonahydrate (0.01 mol) in 10 ml of H₂ O. This mixture was extracted three times with benzene. The benzene solution was dried (CaSO₄). A mixture of 3.03 g of I₂ in 50 ml of benzene was added to this material, dropwise with stirring; stirring was continued for 10 minutes more. It was extracted twice with 10% Na₂ CO₃ and then twice with 5% Na₂ S₂ O₃. The benzene was dried (CaSO₄), concentrated, and the residue redissolved in about 30 ml benzene plus 6.00 g of o-dichlorobenzene (internal gas chromatography standard) and assayed (gas chromatography) for percent product (best yield, 72.0%).

EXAMPLE 52 Preparation of 3-(m-Cumenyl)-4-Isothiazolecarboxylic Acid

To 5.8 g of about 80% pure ethyl β-amino-m-isopropylcinnamate (about 0.02 mol) in 18 ml of DMF was added slowly 2.28 ml (3.82 g, 0.025 mol) of POCl₃ with stirring at -60°. The mixture was allowed to warm; an exothermic reaction carried the temperature to 0°. The mixture was stirred for 10 minutes at 20° and was poured into a cold solution of 7.20 g (0.030 mol) of Na₂ S.9H₂ O in 30 ml of water. This mixture was stirred for 5 minutes and was extracted with three 40-ml portions of benzene. The benzene layers were combined, dried (CaSO₄), treated with 6.35 g (0.025 mol) of I₂ in 120 ml of benzene, stirred for 5 minutes, extracted three times with aqueous NaHCO₃ solution and twice with aqueous sodium thiosulfate solution, and concentrated under vacuum to 6.1 g of an oil that was a 16:84 mixture (gas chromatography assay). The oil was heated with 4.0 g (0.10 mol) of NaOH in 80 ml of 50% aqueous ethanol at reflux for 1 hour. The solution was concentrated under vacuum, diluted with 200 ml of water, extracted three times with ether, and acidified with 17 ml of concentrated HCl (0.20 mol). The resultant mixture was extracted three times with ether. These three ether extracts were combined and concentrated under vacuum. The residue was crystallized from aqueous ethanol to give 2.96 g (60%) of solid, m.p. 143°-157°. The solid was recrystallized from 1,2-dichloroethane to give 2.04 g of solid, m.p. 157°-159°. Recrystallization of this material from 1,2-dichloroethaneheptane (charcoal) gave a white solid, m.p. 158°-160°.

Example 52 illustrates the preparation of the free acid from which the ester may be prepared as illustrated in Example 53. The acid is prepared as an acid to purification.

EXAMPLE 53 Preparation of Ethyl 3-(m-cumenyl)-4-Isothiazolecarboxylate

A mixture of 1.50 g (0.00608 mol) of 3-(m-cumenyl)-4-isothiazolecarboxylic acid and 5 ml (8.2 g, 0.069 mol) of thionyl chloride was heated at reflux on a steam bath for 30 minutes and was concentrated under vacuum. The residue was heated in 15 ml of ethanol at reflux for 15 minutes; the solution was filtered and concentrated under vacuum to 90° (0.3 torr) to give 1.53 g (92%) of oil, n_(D) ²³° =1.5693.

Anal. Calc'd. for C₁₅ H₁₇ NO₂ S: C, 65.43; H, 6.22. Found: C, 65.46; H, 6.30.

EXAMPLE 54 Preparation of 3-(α,α,α-Trifluoro-p-Tolyl)-4-Isothiazolecarboxylic Acid

Using the same procedure of Example 51 but starting with 16.2 g of ethyl β-amino-p-trifluoromethylcinnamate gave 17.09 g of crude ethyl 3-(α,60 ,α-trifluoro-p-tolyl)-4-isothiazolecarboxylate. This material was heated with five equivalents of NaOH in 50 ml of water at reflux for 5 hours. The solution was cooled, extracted with ether, acidified with HCl, and extracted with ether. The latter ether extract was dried (CaSO₄) and concentrated under vacuum. The residue was crystallized three times from 1,2-dichloroethane to give 4.0 g (23%) of solid, m.p. 195°-196°.

Anal. Calc'd. for C₁₁ H₆ F₃ NO₂ S: C, 48.35; H, 2.21. Found: C, 48.39; H, 2.24.

EXAMPLE 55 Preparation of Ethyl 3-(α,α,α-Trifluoro-p-Tolyl)-4-Isothiazolecarboxylate

A solution of 2.5 g (0.0091 mol) of acid and 5.36 g (five equivalents) of thionyl chloride was heated for 0.5 hours on a steam bath and concentrated under vacuum. The residue was heated in 50 ml of ethanol at reflux for 1 hour. Concentration of the solution and crystallization of the residue from ethanol gave 1.41 g (51%) of solid, m.p. 63°-64°.

Anal. Calc'd. for C₁₃ H₁₀ F₃ NO₂ S: C, 51.82; H, 3.35. Found: C, 51.77; H, 3.35.

A third route for the preparation involves the thermolysis of the oxathiazol-2-ones prepared in accordance with Examples 1-5 with alkyl propiolate. Scheme C illustrates this method of preparation. ##STR6##

Scheme C is exemplified below in Examples 56-59.

EXAMPLE 56 Preparation of Ethyl 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylate

A solution of 12.36 g (0.050 mol) of 5-(α,α,α-trifluoro-m-tolyl)-1,3,4-oxathiazol-2-one and 19.62 g (0.20 mol) of ethyl propiolate in 75.0 g of o-dichlorobenzene was held at reflux under N₂ for 20 hours, at which time analysis by gas chromatography revealed that the reaction was complete and that the 4-carboxylate and the 5-carboxylate had formed in 46% and 39% yields, respectively. Concentration of the solution under vacuum gave 16.4 g of dark oil. Crystallization of the oil from 35 ml of ethanol at -20° gave 5.05 g (34%) of tan solid, m.p. 77°-79°, that was about 98% pure 5-carboxylate (gas chromatography assay). Concentration of the filtrate gave 10.8 g of oil. Chromatography of the oil on 550 g of silicic acid with benzene gave 5.2 g of 4-carboxylate that was 97% pure (3% low boilers, no 5-carboxylate present; gas chromatography analysis); infrared (CHCl₃) 5.83μ; nmr (CDCl₃) δ9.43 (s, 1, 5-H), 8.03-7.43 (m, 4, ArH), 4.30 (q, 2, J=7 Hz, OCH₂ CH₃), 1.23 (t, 3, J=7 Hz, OCH₂ CH₃).

Anal. Calc'd. for C₁₃ H₁₀ F₃ NO₂ S: C, 51.82; H, 3.35. Found: C, 52.09; H, 3.50.

The chromatography also gave 0.31 g (2%) of pure 5-carboxylate, m.p. 80°-81.5°. Recrystallization of the 5.05 g of 5-carboxylate from ethanol gave 4.05 g (27%) of colorless crystals, m.p. 80°-81.5°; infrared (CHCl₃) 5.81μ; nmr δ8.20 (s, 1, 4-H), 8.30-7.47 (m, 4, ArH), 4.47 (q, 2, J=7 Hz, OCH₂ CH₃), 1.43 (t, 3, J=7 Hz, OCH₂ CH₃).

Anal. Calc'd. for C₁₃ H₁₀ F₃ NO₂ S: C, 51,82; H, 3.35. Found: C, 51.98; H, 3.39.

EXAMPLE 57 Preparation of Ethyl 3-(-p-Cyanophenyl)-4-Isothiazolecarboxylate

A solution of 10.2 g (0.050 mol) of 5-(p-cyanophenyl)-1,3,4-oxathioazol-2-one and 19.62 g (0.20 mol) of ethyl propiolate in 75.0 g of o-dichlorobenzene was held at reflux under N₂ for 20 hours, at which time gas chromatography analysis indicated that the 4-carboxylate and the 5-carboxylate had formed in 44% and 46% yields, respectively. Concentration of the reaction mixture under vacuum gave 20.3 g of brown solid. Crystallization of this material from ethanol gave 5.54 g (43%) of 5-carboxylate as a beige solid, m.p. 175°-179°. Crystallization of the solid from ethanol gave 0.1 g of unidentified, fairly insoluble white solid, m.p. 236°-237°, infrared (CHCl₃) 4.50, 5.81μ. The residue from the filtrate was chromatographed on silica gel with benzene, and the purest fractions were crystallized from ethanol to give 1.27 g (10%) of 5-carboxylate as a white solid, m.p. 183°-184.5°; infrared (CHCl₃) 4.50, 5.81μ; nmr (CDCl₃) δ8.17 (s, 1, 4-H), 7.93 (AA'BB' m, 4, ArH), 4.43 (q, 2, J=7 Hz, OCH₂ CH₃), 1.40 (t, 3, J=7 Hz, OCH₂ CH₃).

Anal. Calc'd. for C₁₃ H₁₀ N₂ O₂ S: C, 60.45; H, 3.90. Found: C, 60.49; H, 3.98.

The filtrate from the crystallization of the 20.3 g of brown solid was concentrated under vacuum, and the residue was chromatographed on silica gel with benzene. The 4-carboxylate thus obtained was crystallized from heptane to give 4.06 g (32%) of white solid, m.p. 109°-110°; infrared (CHCl₃) 4.50, 5.81μ; nmr (CDCl₃) δ9.40 (s, 1, 5-H), 7.73 (s, 4, ArH), 4.30 (q, 2, J=7 Hz, OCH₂ CH₃), 1.27 (t, 3, J=7 Hz, OCH₂ CH₃).

Anal. Calc'd. for C₁₃ H₁₀ N₂ O₂ S: C, 60.45; H, 3.90. Found: C, 60.48; H, 3.96.

EXAMPLE 58 Preparation of Ethyl 3-(p-Chlorophenyl)-4-Isothiazolecarboxylate

A solution of 10.68 g (0.050 mol) of 5-(-p-chlorophenyl)-1,3,4-oxathiozol-2-one and 19.62 g (0.20 mol) of ethyl propiolate in 75 g of o-dichlorobenzene was held at reflux (150°) under N₂ for 10 hours and was concentrated under vacuum to 90° at 0.2 mm to give 16.0 g of black oil. Dry column chromatography of the oil on silica gel with benzene and crystallizations of the fractions rich in 5-carboxylate gave 3.50 g (26% yield) of pure ethyl 3-(-p-chlorophenyl)-5-isothiazolecarboxylate, m.p. 87.5°-89° (from ethanol); nmr (CDCl₃) δ8.13 (s, 1, 4-H), 7.7 (m, 4, ClC₆ H₄), 4.47 (q, 2, J=7 Hz, OCH₂ CH₃), 1.43 (t, 3, J=7 Hz, OCH₂ CH₃).

Anal. Calc'd. for C₁₂ H₁₀ ClNO₂ S: C, 53.83; H, 3.76. Found: C, 53.84; H, 3.64.

Crystallization of the fractions rich in 4-carboxylate from aqueous ethanol gave 2.45 g (18% yield) of pure ethyl 3-(p-chlorophenyl)-4-isothiazolecarboxylate, m.p. 70.5°-71.5°.

EXAMPLE 59 Preparation of Ethyl 3-(3,5-Dimethoxyphenyl)-4-Isothiazolecarboxylate

By a procedure similar to that employed above, ethyl 3-(3,5-dimethyloxyphenyl)-4-isothiazolecarboxylate was obtained in 25% yield as a white solid, m.p. 71.5°-73° (from ethanol); nmr (CDCl₃) δ9.23 (s, 1, 5-H), 6.72 (d, 2, J=2 Hz, ArH), 6.48 (t, 1, J=2 Hz, ArH), 4.23 (q, 2, J=7 Hz, OCH₂ CH₃), 3.78 (s, 6, OCH₃), 1.23 (t, 3, J=7 Hz, OCH₂ CH₃).

Anal. Calc'd. for C₁₄ H₁₅ NO₄ S: C, 57.32; H, 5.15. Found: C, 57.40; H, 5.21.

Ethyl 3-(3,5-dimethoxyphenyl)-5-isothiazolecarboxylate was obtained in 32% yield as a white solid, m.p. 101°-103° (from ethanol), nmr (CDCl₃) 7.98 (s, 1, 4-H), 7.03 (d, 2, J=2 Hz, ArH), 6.47 (t, 1, J=2 Hz, ArH), 4.37 (q, 2, J=7 Hz, OCH₂ CH₃), 3.82 (s, 6, OCH₃), 1.40 (t, 3, J=7 Hz, OCH₂ CH₃).

Anal. Calc'd. for C₁₄ H₁₅ NO₄ S: C, 57.32; H, 5.15. Found: C, 57.50; H, 5.17.

Another preparation of 3-aryl-4-isothiazolecarboxylates involves the reaction of oxathiazol-2-ones with alkyl chloroacrylate as illustrated by Scheme D. ##STR7##

Example 60 is illustrative of the preparation of 3-aryl-4-isothiazolecarboxylates using the method of Scheme D.

EXAMPLE 60 Preparation of 3-(p-Chlorophenyl)-4-Isothiazolecarboxylates

A solution of 40.4 g (0.30 mol) of ethyl 2-chloroacrylate and 2.14 g (0.010 mol) of 5-(p-chlorophenyl)-1,3,4-oxathiazole-2-one in 75 g of o-dichlorobenzene was held at reflux (165°-175°) for 55 minutes, at which time gas chromatography analysis indicated about 70% reaction. The reaction mixture was allowed to cool, and the supernatant was decanted from polymeric ester. Concentration of the supernatant under vacuum, chromatography of the residue on silicic acid, and crystallizations of the various materials thus obtained gave 0.30 g (16%) of ethyl 3-(p-chlorophenyl)-4-isothiazolecarboxylate, m.p. 69°-70°, and 0.31 g (17%) of ethyl 3-(p-chlorophenyl)-5-isothiazolecarboxylate, m.p. 87°-89°.

Salts of the isoxazole-4-carboxylate acid may be prepared by neutralization of the appropriate acid with the appropriate base. The acid may be prepared in accordance with Scheme A or an ester prepared by any of the other methods may be hydrolyzed to the free acid.

EXAMPLE 61 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Potassium Salt

A solution of 1.91 g (0.0070 mol) carboxylic acid and 0.462 g of 85% KOH (0.0070 mol) in 12 ml of water was concentrated under vacuum to 1.9 g (87%) of white solid, m.p. 276°-277°, infrared (mineral oil mull) 6.30μ.

Anal. Calc'd. for C₁₁ H₅ F₃ KNO₂ S: C, 42.44; H, 1.62. Found: C, 42.51; H, 1.63.

EXAMPLE 62 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Isopropylamine Salt

To a solution of 2.73 g (0.010 mol) of carboxylic acid in 30 ml of ether was added 0.59 g (0.010 mol) of isopropylamine with swirling. After several seconds, copious precipitation of a white solid occurred. The solid was collected and washed with ether to give 2.7 g of white solid, m.p. 145°-147°.

Anal. Calc'd. for C₁₄ H₁₅ F₃ N₂ O₂ S: C, 50.60; H, 4.55. Found: C, 50.57; H, 4.63.

EXAMPLE 63 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Dodecylamine Salt

A solution of 2.70 g (0.0099 mol) of carboxylic acid and 1.83 g (0.0099 mol) of dodecylamine in 30 ml of ether was filtered and concentrated under vacuum to 4.53 g of viscous oil that slowly crystallized, m.p. 43°-45°.

Anal. Calc'd. for C₂₃ H₃₃ F₃ N₂ O₂ S: C, 60.24; H, 7.25. Found: C, 60.05; H, 7.12.

Additionally, esters have been prepared from the free acid prepared in accordance with Scheme A. These esters have been prepared by various procedures illustrated by Examples 64-67.

EXAMPLE 64 Preparation of Ethyl 3-(p-Tolyl)-4-Isothiazolecarboxylate

3-(p-Tolyl)-4-isothiazolecarboxylic acid (1.5 g, 0.0068 mol), 20 ml of absolute ethanol, and boron trifluoride etherate (4.3 ml, 0.034 mol) were heated at reflux for 24 hours. Volatile materials were removed under reduced pressure. Water (25 ml) was added and the material extracted four times with ether. The ether was back-extracted with 5% NaHCO₃, dried (CaSO₄) and concentrated under reduced pressure to yield 1.51 g (0.0061 mol, 89.9%) of oil, n_(D) ²⁵ =1.5671.

Anal. Calc'd. for C₁₃ H₁₃ NO₂ S: C, 63.13; H, 5.30. Found: C, 62.95; H, 5.52.

EXAMPLE 65 Preparation of Ethyl 3-(p-Nitrophenyl)-4-Isothiazolecarboxylate

3-(p-Nitrophenyl)-4-Isothiazolecarboxylic acid (1.5 g, 0.006 mol), plus one equivalent (2.51 g) of benzyl trimethylammonium hydroxide (40% in methanol) and excess ethyl iodide were heated just to reflux in hexamethylphoramide. The product was recrystallized twice from ethanol to yield 0.24 g (0.00086 mol, 14.3%) of ester, m.p. 150.5°-152.5°.

Anal. Calc'd. for C₁₂ H₁₀ N₂ O₄ S: C, 51.79; H, 3.62. Found: C, 52.35; H, 3.70.

EXAMPLE 66 Preparation of Glycolic Acid, Ethyl Ester, 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylate

To a mixture of 1.36 g (0.0050 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarboxylic acid in 10 ml of hexamethylphosphoric triamide was added 0.80 g of 50% NaOH (0.010 mol), followed by 3.1 g (0.0254 mol) of ethyl chloroacetate. The mixture was stirred vigorously for 18 hours, diluted with water, and extracted twice with 40-ml portions of ether. The combined ether layers were washed twice with water, three times with aqueous K₂ CO₃ solution, again with water, dried (CaSO₄), and concentrated under vacuum to 90° at 0.3 torr to give 1.5 g of 87% pure product as an oil. This oil was chromatographed on 130 g of Woelm silica gel (for dry column chromatography) in a 30 mm diameter column with 30% CHCl₃ in benzene. There was obtained 0.43 g of colorless liquid, n_(D) ²².8° =1.5241, that was 100% pure product.

Anal. Calc'd. for C₁₅ H₁₂ F₃ NO₄ S: C, 50.14; H, 3.37. Found: C, 50.06; H, 3.28.

EXAMPLE 67 Preparation of Lactic Acid, Ethyl Ester, 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic

By a procedure similar to that used for Example 66, there was obtained 1.7 g of oil, n_(D) ²³ =1.5169 (yield 66.5%).

Anal. Calc'd. for C₁₆ H₁₄ F₃ NO₄ S: C, 51.47; H, 3.78; N, 3.75. Found: C, 51.20; H, 3.48; N, 3.73.

3-Phenyl-4-isothiazolecarbonyl chlorides may be prepared by reaction of the free acid with thionyl chloride as discussed in Scheme A.

EXAMPLE 68 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarbonyl Chloride

A mixture of 27.3 g (0.10 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarboxylic acid and 20 ml (32.8 g, 0.276 mol) of thionyl chloride (purified by distillation from a little triphenyl phosphite) was heated on a steam bath for 40 minutes and then was concentrated under vacuum to remove excess SOCl₂. The resultant 27.3 g of product was crystallized from heptane to give 25.5 g (87%) of white solid, m.p. 76°-77.5°, infrared (CH₂ Cl₂) 5.70μ.

Anal. Calc'd. for C₁₁ H₅ ClF₃ NOS: C, 45.30; H, 1.73. Found: C, 45.41; H, 1.65.

3-Phenyl-4-isothiazolecarboxamides may be prepared by reaction of the acid chloride with ammonia or the appropriate amine.

EXAMPLE 69 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxamide

A solution of 2.92 g (0.010 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride in 10 ml of THF was added to a solution of excess ammonia gas in THF stirred in a dry ice acetone bath. The mixture was slowly warmed to 23° with stirring. The solid NH₄ Cl was removed by filtration, and the filtrate was concentrated to about 20 ml. Then 100 ml of ether was added, and the solution was extracted with two portions of 10% Na₂ CO₃ solution and once with saturated NaCl solution. The ether layer was dried (CaSO₄) and concentrated to 2.25 g (83%) of white solid, m.p. 141°-141.5°; infrared (mineral oil mull) 2.92, 3.11, 6.09, 6.11μ.

Anal. Calc'd. for C₁₁ H₇ F₃ N₂ OS: C, 48.53; H, 2.59. Found: C, 48.73; H, 2.75.

EXAMPLE 70 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Isopropyl Amide

To a solution of 1.0 g (0.0034 mol) of 3-(α,α,α-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride and 20 cc of THF was added 0.45 g (2.1 equivalents) of isopropylamine. The reaction mixture was heated on a steam bath for 20 minutes. The isopropylamine hydrochloride was filtered off and the filtrate was concentrated to a solid. The solid was washed with H₂ O, dissolved in THF, dried (CaSO₄), and concentrated under vacuum to give 0.94 g of solid. The solid was recrystallized from EtOAc/hexane to give 0.4 g white solid, m.p. 166°-167°. The filtrate gave another 0.3 g of white solid, m.p. 166.5°-168°. (Total yield=88%).

Anal. Calc'd. for C₁₄ H₁₃ F₃ N₂ OS: C, 53.50; H, 4.17; N, 8.91. Found: C, 53.61; H, 4.10; N, 8.92.

EXAMPLE 71 Preparation of 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Diethylamine

By a procedure similar to that used for Example 70, there was obtained 0.97 g of a yellow oil, n_(D) ²³ =1.5383. (yield 86.9%).

Anal. Calc'd. for C₁₅ H₁₅ F₃ N₂ OS: C, 54.87; H, 4.60; N, 8.53. Found: C, 54.93; H, 4.96; N, 8.59.

The isoxazolecarboxylates of the foregoing formula can be prepared by 1,3-dipolar cycloaddition of nitrile oxides, formed in situ from hydroxamoyl chlorides, to alkyl β-pyrrolidinylacrylates. Scheme E illustrates the preparation of said isoxazolecarboxylates. ##STR8##

Alkyl β-pyrrolidinylacrylates may be prepared by the addition of pyrrolidine to alkyl propiolate. Hydroxamoyl chloride may be prepared by the addition of chlorine to the appropriate benzaldoxime.

Examples 72-79 are presented in order to illustrate the preparation of the isoxazolecarboxylates of the invention.

EXAMPLE 72 Preparation of Ethyl β-Pyrrolidinylacrylate

A solution of 29.43 g of ethyl propiolate (0.30 mol) in 200 ml of benzene was held at 25° in a water bath with magnetic stirring. A solution of 21.34 g of pyrrolidine in 50 ml of benzene was added dropwise over a period of 45 minutes, during which time the temperature rose to 35°. The clear brown solution was stirred overnight and the solvent removed under reduced pressure at 55°. The residue was distilled under pressure to give 35.05 g of yellow oil, boiling point 110° (0.4 torr), which crystallized upon standing. The yellow solid was recrystallized from petroleum ether to give 31.36 (62%) of yellowish platelets, m.p. 37.5°-39.5°.

EXAMPLE 73 Preparation of m-Trifluoromethylbenzohydroxamoyl Chloride

A solution of 15.70 g of m-trifluoromethylbenzaldoxime (0.082 mol) in 40 ml of chloroform was cooled with magnetic stirring to -5° in ice-MeOH. A gentle stream of Cl₂ was passed into the solution, while the temperature was maintained below 0°, until addition of more Cl₂ did not produce a green color. The mixture was stirred for two hours and allowed to warm to room temperature. The solvent was removed by evaporation under reduced pressure at 50° and the oily product recrystallized twice from petroleum ether, to give 13.69 g (70%) of tan needles, m.p. 52.5°-54°; infrared (melt) 3400 cm, 1600 (m), 1430 (m), 1325 (s), nmr (CCl₄) δ8.64 (s, 1H) and δ7.3-8.2 (m, 4H).

Anal. Calc'd. for C₈ H₅ ClF₃ NO: C, 42,98; H, 2.25; Cl, 15.86; N, 6.26. Found: C, 42.98; H, 2.32; Cl, 16.13; N, 6.27.

Other hydroxamoyl chlorides prepared by this procedure were: benzohydroxamoyl chloride, m.p. 42°; p-chlorobenzohydroxamoyl chloride, m.p. 82°-84°; m-chlorobenzohydroxamoyl chloride, m.p. 61°-63°; m-nitrobenzohydroxamoyl chloride, m.p. 98°-101°.

EXAMPLE 74 Preparation of Ethyl 3-(α,α,α-Trifluoro-m-Tolyl)-4-Isoxazolecarboxylate

A solution of 4.87 g of ethyl β-pyrrolidinylacrylate (0.0288 mol) and 5.0 ml of triethylamine in 60 ml of ethyl ether was cooled to 0°. A solution of 6.43 g of m-trifluoromethylbenzohydroxamoyl chloride in 25 ml of ether was added over a period of 45 minutes with magnetic stirring, during which time a white precipitate of Et₃ N.HCl formed. The mixture was stirred at 0° for 2.5 hours and filtered and the solid washed thoroughly with ether. The combined solutions were washed with 5% HCl and water, dried over MgSO₄, filtered and concentrated to 7.66 g of orange oil, only one peak was observed on GLC. Double distillation through a 4"×1/2" Vigreux column gave 5.95 g (72% crude), boiling point 98°-100° (0.08 torr), slightly yellow oil, tlc (Silica Gel G, benzene) showed 3 spots, R_(f) 0.21, 0.46, and 0.61. Chromatography of 5.80 g of the oil on 110 g of dry column silica gel (˜80 cm long) gave 1.79 g of oil (mixture R_(f) 0.46 and 0.61, faint), first 120 ml benzene eluent and 3.78 g clear colorless oil in the second 120 ml benzene (pure by tlc, R_(f) 0.46). The second fraction was distilled giving 2.85 g (34%) of pure product, boiling point 94° (0.045 torr), infrared (neat); 1720 cm⁻¹ (s), 1340 (s), 1120 (s); nmr (CCl₄) δ1.25 (t, 3H), 4.26 (q, 2H), 7.4-8.2 (m, 4H) and 9.0 (s, 1H).

Anal. Calc'd. for C₁₃ H₁₀ F₃ NO₂ : C, 54.74; H, 3.53; F, 19.98; N, 4.91. Found: C, 54.68; H, 3.39; F, 19.87; N, 5.00.

EXAMPLE 75 Preparation of Ethyl 3-(4-Chlorophenyl)-4-Isoxazolecarboxylate

The crude product from the reaction of 4.23 g of ethyl β-pyrrolidinylacrylate (0.025 mol) and the nitrile oxide from 4.75 g p-chlorobenzohydroxamoyl chloride (0.025 mol) and 3.5 ml Et₃ N run as above, gave, after chromatography, 1.27 g (20%) of white solid, m.p. 43°-45°; infrared (melt); 1725 cm⁻¹ (s), 1290 (s) and 1170 (s); nmr (CCl₄) δ1.35 (t, 3H), 4.30 (q, 2H), 7.4 and 7.8 (ABq, 4H) and 8.95 (s, 1H).

Anal. Calc'd. for C₁₂ H₁₀ ClNO₃ : C, 57.27; H, 4.01; Cl, 14.09; N, 5.57. Found: C, 57.29; H, 3.88; Cl, 14.04; N, 5.35.

EXAMPLE 76 Preparation of Ethyl 3-(3-Chlorophenyl)-4-Isoxazolecarboxylate

The crude oil from the reaction of 4.23 g of ethyl β-pyrrolidinylacrylate (0.025 mol) and the nitrile oxide from 4.75 g of 3-chlorobenzohydroxamoyl chloride and 3.5 ml of Et₃ N, run as in Example 74, was twice crystallized from petroleum ether to give 2.78 g (44%) of tan powder, m.p. 43°-45°; infrared (melt); 1720 cm⁻¹ (s), 1550 (s), 1290 (s), 1125 (s); nmr (CCl₄) δ1.35 (t, 3H), 4.25 (q, 2H), 7.2-7.4 and 7.5-7.9 (complex, 4H), 8.95 (s, 1H).

Anal. Calc'd. for C₁₂ H₁₀ ClNO₃ : C, 57.27; H, 4.01; Cl, 14.09; N, 5.57. Found: C, 57.07; H, 4.02; Cl, 13.99; N, 5.67.

EXAMPLE 77 Preparation of Ethyl 3-(3-Nitrophenyl)-4-Isoxazolecarboxylate

A mixture of 4.23 g (0.025 mol) of ethyl β-pyrrolidinylacrylate and 3.5 ml of triethylamine in 60 ml of anhydrous ether was cooled to -10°. A solution of 5.01 g (0.025 mol) of 3-nitrobenzohydroxamoyl chloride in 20 ml of ether was added dropwise in 30 minutes with rapid magnetic stirring. The mixture was stirred at -10°-0° for 4 hours and allowed to warm to room temperature overnight. The solid was removed by filtration and washed four times with 50 ml of boiling ether. The residues from the evaporation of the ether solutions were recrystallized from hexane and combined to give 3.72 g (58%) of white needles, m.p. 90°-92°; nmr (CCl₄) δ1.30 (t, 3H), 4.27 (q, 2H), 7.47-8.80 (m, 4H) and 9.06 (s, 1H).

Anal. Calc'd. for C₁₂ H₁₀ N₂ O₅ : C, 54.97; H, 3.84; N, 10.68. Found: C, 55.07; H, 3.91; N, 10.59.

EXAMPLE 78 Preparation of Ethyl 3-(3-Cyanophenyl)-4-Isoxazolecarboxylate

A solution of 8.46 g (0.05 mol) of β-pyrrolidinylacrylate and 9.05 g (0.05 mol) of 3-cyanobenzohydroxamoyl chloride in 175 ml of ether was cooled to -15°. A solution of 7.0 ml of triethylamine in 15 ml of ether was added dropwise with magnetic stirring over 40 minutes. A dense white precipitate formed immediately. The mixture was stirred at 0° for 3 hours and allowed to warm to room temperature overnight. The dense suspension was thoroughly mixed with 400 ml of methylene chloride. The suspension was washed twice with water and twice with 6 N HCl. The aqueous solution was back-extracted with four 50-ml portions of methylene chloride. The combined organic solutions were washed with water and dried over anhydrous sodium sulfate, filtered, and concentrated to a nearly white solid. Recrystallization from benzene-hexane gave 9.57 g (79%) of slightly yellow needles, m.p. 135°-7°; infrared (KBr) 2245 cm⁻¹, nmr (CDCl₃) δ 1.37 (t, 3H), 4.40 (q, 2H), 7.6-8.3 (m, 4H) and 9.13 (s, 1H).

Anal. Calc'd. for C₁₃ H₁₀ N₂ O₃ : C, 64.46; H, 4.16; N, 11.56. Found: C, 64.49; H, 4.12; N, 11.56.

EXAMPLE 79 Preparation of Ethyl 3-Phenyl-4-Isoxazolecarboxylate

Utilizing the procedure of Example 78 with benzohydroxamoyl chloride as a reactant in lieu of 3-cyanobenzohydroxamoyl chloride, ethyl 3-phenyl-4-isoxazolecarboxylate was prepared as a crude oil.

Anal. Calc'd. for C₁₂ H₁₁ NO₃ : C, 66.35; H, 5.10; N, 6.45. Found: C, 66.22; H, 5.09; N, 6.55.

Haloalkyl esters may be prepared from the free acid in accordance with Example 80.

EXAMPLE 80 Preparation of 2,2,2-Trifluoromethyl-3-(α,α,α-Trifluoro-m-Tolyl)-4-Isoxazolecarboxylate

A solution of 2.85 g ethyl ester prepared by Example 74 in 10 ml glacial acetic acid and 10 ml concentrated HCl was heated at reflux for 4 hours. The solution was cooled and most of the solvent removed by evaporation under reduced pressure. The pasty residue was washed with water and dried giving 2.2 g (85%) of acid, m.p. 115°-118°.

A solution of 5.31 g of the acid in 15 ml of thionyl chloride was heated at reflux for 1 hour. The excess thionyl chloride was removed by evaporation under reduced pressure giving 5.70 g of crude acid chloride (nmr showed no acid proton) which was used immediately in the following two reactions.

The crude acid chloride, 1.70 g, was stirred at room temperature with 5 ml of 2,2,2-trifluoroethanol for 1 hour and then heated at reflux for 2 hours. The excess alcohol was removed by evaporation to give a brown oil. The nmr spectrum showed two isoxazole ring protons indicating incomplete reaction. The mixture was dissolved in 5 ml 2,2,2-trifluoroethanol and heated at reflux for two hours and stirred at room temperature overnight. After removal of excess alcohol, the yield was 1.55 g of brown oil which was chromatographed on 25 g silica gel. Elution with 50 ml of 1:1 hexane-ether gave 1.51 g ester. Distillation gave 0.620 g pure ester, boiling point 88° 0.1 torr; nmr (CCl₄) δ4.56 (q, 2H), 7.3-8.2 (m, 4H) and 9.05 (s, 1H).

Anal. Calc'd. for C₁₃ H₇ F₆ NO₃ : C, 46.03; H, 2.08; F, 33.61; N, 4.13. Found: C, 46.22; H, 2.03; F, 33.86; N, 4.28.

The isothiazolecarboxylates and the isoxazolecarboxylates of the present invention have been found to be effective in inhibiting the growth of undesirable plants. They are especially effective when applied to the soil before emergence of the undesirable plants. When tested in accordance with the procedures described below, some selectivity, i.e., reduction in herbicidal injury, was found with respect to narrowleaf crops such as wheat.

As used herein, the term "active ingredient" is understood to mean an isothiazolecarboxylate or isoxazolecarboxylate of the foregoing formula (I).

To illustrate the herbicidal properties of the compounds of the present invention, said compounds were tested in the following manner.

The pre-emergent test was conducted as follows.

A good grade of top soil was placed in aluminum pans and compacted to a depth of three-eighths to one-half inch from the top of the pan. On the top of the soil was placed a predetermined number of seeds or vegetative propagules of various plant species. The soil required to level fill the pans after seeding or adding vegetative propagules was weighed into a pan. A known amount of the active ingredient applied in a solvent or as a wettable powder and the soil were thoroughly mixed, and used as a cover layer for prepared pans. After treatment the pans were moved into a greenhouse bench where they were watered from below as needed to give adequate moisture for germination and growth.

Unless noted otherwise, approximately 4 weeks after seeding and treating, the plants were observed to determine all deviations from the normal growth habit and the results recorded. A herbicidal rating code was used to signify the extent of phytotoxicity of each species. The ratings are defined as follows:

    ______________________________________                                         % Control     Rating                                                           ______________________________________                                          0-24         0                                                                25-49         1                                                                50-74         2                                                                 75-100       3                                                                ______________________________________                                    

The plant species utilized in these tests are identified by letter in accordance with the following legend:

    ______________________________________                                         A-Canada Thistle  K-Barnyard Grass                                             B-Cocklebur       L-Soybean                                                    C-Velvetleaf      M-Sugar Beet                                                 D-Morning Glory   N-Wheat                                                      E-Lambsquarters   O-Rice                                                       F-Smartweed       P-Sorghum                                                    G-Nutsedge        Q-Wild Buckwheat                                             H-Quackgrass      R-Hemp Sesbania                                              I-Johnson Grass   S-Panicum Spp                                                J-Downy Brome     T-Crabgrass                                                  ______________________________________                                    

Results of the pre-emergent tests are summarized in Tables I and II, below.

                  TABLE I                                                          ______________________________________                                         Com-                                                                           pound                                                                          of                                                                             Ex-                                                                            ample Rate     Plant Species                                                   No.   (kg/h)   A     B   C   D   E   F   G   H   I   J                                                      K                                                 ______________________________________                                         26    11.2     3     0   1   3   3   --  1   0   0   0                                                      3                                                                              26 5.6 1 0 0 1 3 -- 1 0 0 0 3                                                  27 11.2 1 1 3 3 3 -- 0 1 0 3 3                                                 27 5.6 1 0 0 1 3 -- 0 0 0 0 3                                                  28 11.2 3 0 0 2 3 -- 0 1 2 3 3                                                 28 5.6 1 0 1 2 3 -- 0 0 0 3 3                                                  29 11.2 0 0 0 1 0 0 0 0 0 0 0                                                  30 11.2 3 2 3 2 3 -- 3 3 2 3 3                                                 30 5.6 3 2 2 2 2 -- 2 2 1 2 3                                                  31 11.2 2 0 0 0 1 -- 1 1 0 1 3                                                 31 5.6 0 0 0 0 1 -- 0 2 0 0 2                                                  32 11.2 3 2 3 3 3 1 3 1 1 1 3                                                  32 5.6 3 1 3 3 2 2 3 1 1 0 3                                                   33 11.2 3 1 2 2 2 3 2 2 0 1 3                                                  33 5.6 3 1 1 2 3 1 3 0 2 0 3                                                   34 11.2 3 2 2 3 3 2 3 3 3 2 3                                                  34 5.6 3 2 2 1 3 2 1 1 0 1 3                                                   35 11.2 3 1 1 1 2 1 1 1 2 0 3                                                  35 5.6 2 -- 0 1 3 2 0 0 0 0 3                                                  36 11.2 3 2 2 1 3 3 2 1 0 1 3                                                  36 5.6 3 1 1 1 1 0 1 1 0 0 3                                                   37 11.2 3 3 2 2 3 2 3 2 1 1 3                                                  37 5.6 3 2 0 1 3 2 2 2 3 1 3                                                   38 11.2 3 -- 2 2 3 3 2 1 3 2 3                                                 38 5.6 2 -- 3 2 3 3 2 3 3 1 3                                                   39* 11.2 1 1 0 0 2 2 0 0 0 0 1                                                 39* 5.6 1 0 0 0 0 1 0 0 1 0 0                                                 40 11.2 3 -- 2 3 3 -- 3 3 3 3 3                                                40 5.6 3 -- 1 3 3 -- 3 3 3 1 3                                                 41 11.2 3 2 2 3 3 -- 3 3 3 2 3                                                 41 5.6 3 2 1 2 2 -- 3 2 3 1 3                                                  42 11.2 3 3 2 2 2 -- 3 3 1 2 3                                                 42 5.6 3 1 0 2 1 -- 3 1 1 0 3                                                  43 11.2 3 2 1 2 1 -- 1 0 3 0 3                                                 43 5.6 2 0 1 1 1 -- 0 0 0 0 3                                                  44 5.6 3 2 2 2 2 3 1 0 0 1 3                                                   45 11.2 0 0 0 1 1 0 0 0 0 0 1                                                  45 5.6 1 1 0 1 0 0 0 0 0 0 1                                                   51 5.6 2 0 0 1 1 3 0 2 2 0 2                                                   53 11.2 3 1 0 1 2 1 3 1 0 0 3                                                  53 5.6 2 1 1 0 3 0 3 0 0 0 3                                                   55 11.2 3 3 3 3 3 2 2 2 0 3 3                                                  55 5.6 3 1 1 3 1 1 1 0 0 0 2                                                   56 5.6 3 0 1 2 2 3 2 3 3 0 3                                                   57 11.2 1 0 0 1 0 -- 0 0 -- 0 0                                                58 5.6 3 0 0 3 0 -- 0 1 0 0 2                                                  59 5.6 1 0 0 1 0 0 0 0 0 0 0                                                   64 11.2 2 -- 1 3 3 -- 0 1 0 0 3                                                65 11.2 1 -- 0 1 0 -- 0 0 0 0 0                                                66 11.2 3 2 3 3 3 1 3 1 3 0 3                                                  66 5.6 3 1 1 2 1 1 1 0 3 0 3                                                   67 11.2 3 2 1 3 2 3 2 1 3 0 3                                                  67 5.6 3 1 1 2 2 1 2 1 2 0 3                                                   68 11.2 3 2 1 2 2 -- 1 0 0 0 3                                                 68 5.6 3 2 2 1 3 --  3 1 2 0 3                                                 69 11.2 2 -- 1 2 3 -- 0 0 0 1 1                                                 70* 11.2 0 -- 0 0 0 0 0 0 0 0 0                                                70* 5.6 0 0 0 0 0 0 0 0 0 0 0                                                  71* 11.2 0 0 0 0 0 0 3 0 0 0 1                                                 71* 5.6 1 0 0 0 0 0 0 0 0 0 0                                                  71* 5.6 3 0 0 1 3 3 1 0 0 0 0                                                 74 11.2 3 3 1 3 3 2 2 3 3 3 3                                                  74 5.6 3 2 1 1 2 0 1 3 3 3 3                                                   75 11.2 3 0 0 1 1 1 0 1 0 0 1                                                   75* 5.6 1 0 0 0 0 0 0 3 0 0 1                                                 76 11.2 3 0 2 3 3 3 0 1 0 0 3                                                  76 5.6 2 0 0 1 3 0 0 3 0 0 3                                                    77* 11.2 0 0 0 3 0 0 0 0 0 0 0                                                 77* 5.6 0 3 0 0 0 0 0 0 0 0 0                                                 78 11.2 2 1 1 1 1 0 0 0 0 0 0                                                   78* 5.6 1 0 1 1 0 0 0 0 0 0 0                                                 80 11.2 3 2 2 3 1 2 1 3 0 3 3                                                  80 5.6 3 0 1 0 0 0 1 3 0 2 1                      ______________________________________                                          *plants observed 2 weeks after treatment.                                

                                      TABLE II                                     __________________________________________________________________________     Com-                                                                           pound                                                                          of Ex.                                                                               Rate Plant Species                                                       Number                                                                               (kg/h)                                                                              L M N O P B Q D R E F C J S K T                                     __________________________________________________________________________     26    5.6  0 2 1 0 0 0 0 1 1 0 --                                                                               0 0 0 3 3                                     26    1.12 0 0 0 0 0 1 0 1 0 0 --                                                                               0 0 0 0 0                                     27    11.2 0 3 1 0 1 0 0 2 3 3 3 1 2 1 3 3                                     27    8.4  0 2 0 0 0 0 0 2 1 3 1 1 0 1 3 3                                     27    5.6  0 3 1 1 1 0 1 2 2 2 --                                                                               2 1 3 3 3                                     27    1.12 0 0 0 1 0 0 0 0 0 0 --                                                                               0 0 0 0 1                                     28    5.6  0 2 0 0 0 0 0 1 2 2 --                                                                               1 0 2 3 3                                     28    1.12 0 0 0 0 0 0 0 0 0 0 --                                                                               0 0 1 1 3                                      28*  0.28 0 0 0 0 0 0 0 0 0 0 --                                                                               0 1 0 0 1                                     30    5.6  3 3 1 3 3 2 3 2 3 2 --                                                                               2 2 3 3 2                                     30    1.12 1 3 0 3 2 1 1 2 2 2 --                                                                               2 0 2 3 1                                     30    0.28 0 2 0 0 0 1 0 2 0 1 --                                                                               0 0 2 1 0                                      31*  5.6  1 2 2 2 3 1 0 3 1 1 --                                                                               1 2 3 3 3                                      31*  1.12 0 0 0 0 0 0 0 0 0 0 --                                                                               0 0 0 1 0                                     32    5.6  2 3 0 2 3 2 3 3 3 3 3 3 2 3 3 3                                     32    1.12 1 2 0 1 3 1 0 3 2 2 1 1 0 2 3 1                                     32    0.25 0 2 0 0 0 1 0 0 0 0 0 0 0 0 1 1                                     33    5.6  0 2 0 1 3 1 2 2 1 1 1 2 1 1 3 1                                      33*  1.12 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0                                     34    5.6  3 3 0 3 3 1 3 2 2 3 2 1 1 3 3 3                                      34*  1.12 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 1                                     35    5.6  2 1 0 1 3 --                                                                               0 1 1 0 0 1 0 2 3 2                                      35** 1.12 0 1 0 0 0 --                                                                               0 0 0 0 0 0 0 0 0 0                                     36    5.6  1 2 0 1 2 0 2 1 1 2 1 1 1 2 3 3                                      36*  1.12 0 1 0 0 0 0 0 0 0 0 0 1 0 1 2 0                                     37    5.6  1 2 0 1 3 --                                                                               1 2 1 2 1 0 1 3 3 3                                     37    1.12 1 1 0 0 0 --                                                                               1 0 3 2 1 0 0 0 1 0                                      37*  0.28 2 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0                                     38    5.6  3 3 0 3 3 --                                                                               1 3 2 2 2 1 0 2 3 3                                     38    1.12 1 2 0 0 0 --                                                                               0 3 0 0 0 1 0 0 3 1                                      38*  0.28 0 1 0 0 0 --                                                                               0 1 0 0 0 0 0 0 0 0                                     40    5.6  2 2 1 3 3 2 3 3 3 2 --                                                                               1 2 3 3 3                                     40    1.12 1 1 0 1 3 1 1 1 2 1 --                                                                               0 1 3 3 2                                     41    5.6  2 3 1 2 3 2 2 2 3 2 --                                                                               1 1 3 3 3                                     41    1.12 0 1 0 1 2 2 1 1 1 2 --                                                                               0 0 3 3 1                                     42    5.6  0 2 0 1 3 1 2 2 1 2 --                                                                               1 1 3 3 1                                     42    1.12 0 1 0 0 0 0 0 0 0 0 --                                                                               0 0 0 3 1                                     43    5.6  0 2 1 2 2 1 0 1 1 3 --                                                                               2 0 1 3 1                                     43    1.12 0 1 0 0 0 0 0 0 0 0 --                                                                               0 0 0 0 0                                      44*  1.12 1 1 0 0 0 0 0 0 0 1 0 0 0 0 3 0                                     51    1.12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0                                      51*  0.28 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0                                     53    5.6  2 3 0 1 3 2 1 2 2 2 0 0 0 3 3 1                                     53    1.12 1 2 0 1 0 0 0 1 1 1 0 0 0 1 3 0                                     55    5.6  3 2 0 0 2 2 0 3 2 2 1 1 0 0 3 3                                     55    1.12 1 1 0 0 0 1 1 1 3 1 1 0 0 0 0 0                                     56    1.12 1 2 1 0 2 3 0 2 1 1 1 1 1 2 3 1                                     56    0.56 0 2 0 0 2 0 0 0 0 1 --                                                                               0 0 1 3 0                                      58*  1.12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0                                     64    5.6  1 2 1 1 2 1 0 2 1 2 --                                                                               1 0 0 3 2                                     64    1.12 0 1 0 0 0 0 0 0 0 1 --                                                                               0 0 0 3 0                                     66    5.6  1 3 0 2 3 2 2 2 3 2 2 2 0 3 3 0                                     66    1.12 1 2 0 0 0 1 0 0 1 0 0 1 0 0 0 0                                     67    5.6  1 2 0 0 3 1 2 3 2 2 1 1 1 3 3 1                                      67*  1.12 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0                                     68    1.12 0 2 1 1 3 1 2 3 1 3 --                                                                               1 0 1 2 1                                      69*  5.6  0 0 0 0 0 0 0 0 0 0 --                                                                               0 0 0 0 0                                     74    5.6  2 3 3 3 3 1 3 1 3 1 2 2 3 3 3 3                                     74    1.12 1 1 1 1 1 0 0 0 2 0 0 1 3 1 1 2                                     76    5.6  2 2 0 1 0 0 0 1 3 2 0 1 0 0 3 0                                     80    5.6  1 1 1 3 2 1 0 1 3 0 0 2 3 3 3 1                                     80    1.12 0 0 0 1 0 --                                                                               0 0 0 0 0 0 0 0 0 0                                     __________________________________________________________________________      *plants observed 2 weeks after treatment.                                      **plants observed 3 weeks after treatment.                               

The post-emergent tests were conducted as follows.

The active ingredients are applied in spray form to two or three-week old specimens of various plant species. The spray, a solution or wettable powder suspension containing the appropriate rate of active ingredient to give the desired test rate and a surfactant, is applied to the plants. The treated plants are placed in a greenhouse and unless otherwise noted approximately four weeks later the effects are observed and recorded. The results are shown in Tables III and IV in which the post-emergent herbicidal rating code is as follows:

    ______________________________________                                         % Control            Rating                                                    ______________________________________                                          0-24                0                                                         25-49                1                                                         50-74                2                                                         75-99                3                                                         100                  4                                                         ______________________________________                                    

The plant species utilized in these tests are identified by letter in accordance with the previous legend.

                  TABLE III                                                        ______________________________________                                         Com-                                                                           pound                                                                          of Ex-                                                                         ample Rate     Plant Species                                                   No.   (kg/h)   A     B   C   D   E   F   G   H   I   J                                                      K                                                 ______________________________________                                          26*  11.2     0     0   0   0   0   --  0   0   0   0                                                      0                                                                               27* 11.2 2 1 1 0 0 -- 0 0 0 0 0                                               28 11.2 2 1 1 1 0 -- 0 0 0 0 0                                                  29* 11.2 0 0 0 0 0 0 0 0 0 0 0                                                30 11.2 1 1 1 1 1 -- 0 0 0 0 0                                                 31 11.2 1 1 1 1 1 -- 1 0 0 0 0                                                 32 11.2 2 2 2 2 1 0 0 0 0 0 0                                                  33 11.2 3 2 2 3 2 2 1 1 0 0 0                                                  33 4.48 2 2 2 3 2 1 0 1 0 0 0                                                  34 11.2 2 2 2 2 1 1 0 0 1 0 0                                                  35 11.2 1 2 1 3 2 1 1 1 1 0 1                                                  36 11.2 2 2 1 2 2 1 1 0 0 0 1                                                   37* 11.2 2 1 1 2 3 0 0 0 0 0 0                                                 37* 4.48 1 1 0 1 3 0 0 0 0 0 0                                                38 11.2 2 2 2 3 2 2 1 1 0 0 2                                                   39* 11.2 0 1 0 1 3 0 -- 0 0 0 0                                               40 11.2 3 -- 1 2 1 -- 1 1 0 0 0                                                40 4.48 2 1 -- 2 2 -- 1 0 2 3 1                                                41 11.2 2 2 1 3 1 -- 0 0 0 0 0                                                 42 11.2 2 2 1 2 1 -- 1 1 0 0 2                                                 43 11.2 2 2 2 2 2 -- 1 0 0 0 0                                                 44 11.2 1 1 1 1 0 -- 0 0 0 0 0                                                  45* 11.2 0 0 0 0 0 0 0 0 0 0 0                                                 51* 4.48 0 0 0 0 2 0 -- 0 0 0 0                                                53* 11.2 1 0 0 1 1 0 0 0 0 0 0                                                55 11.2 0 0 0 1 1 0 0 0 0 0 0                                                  56 4.48 1 1 1 1 2 1 0 0 0 0 0                                                   57* 11.2 0 0 0 0 0 -- 0 0 0 0 0                                               58 4.48 0 0 0 0 0 -- 0 0 0 0 0                                                  59* 4.48 0 0 0 0 0 -- 0 0 0 0 0                                                64* 11.2 0 -- 0 0 0 -- 0 0 0 0 0                                              65 11.2 1 -- 0 2 2 -- 0 0 0 0 0                                                66 11.2 3 2 2 3 1 0 0 0 0 0 0                                                  66 4.48 1 2 1 2 1 0 0 0 0 0 0                                                  67 11.2 2 2 2 2 1 -- 0 0 0 0 0                                                 68 11.2 -- 2 2 2 1 -- 0 0 0 0 2                                                68 4.48 4 2 2 2 1 -- 1 0 -- 0 0                                                69 11.2 1 -- 0 1 1 -- 0 0 0 0 0                                                 70* 11.2 --  0 1 1 3 0 0 0 0 0 0                                               70* 4.48 0 1 0 1 1 0 0 0 0 0 0                                                 71* 11.2 0 -- 0 1 4 0 0 0 0 0 0                                               74 11.2 2 1 1 1 1 -- 0 0 0 0 0                                                  75* 11.2 -- 0 0 1 0 0 0 0 0 0 0                                               76 11.2 2 1 1 1 1 -- 0 0 1 0 0                                                 77 11.2 0 1 0 1 0 0 0 0 0 0 0                                                  78 11.2 0 1 0 2 1 0 0 0 0 0 0                                                  80 11.2 2 2 2 3 1 0 0 0 0 0 1                     ______________________________________                                          *plants observed 2 weeks after treatment.                                

                                      TABLE IV                                     __________________________________________________________________________     Com-                                                                           pound                                                                          of Ex.                                                                              Rate                                                                               Plant Species                                                         Number                                                                              (kg/h)                                                                             L M N O P B Q D R E F C J S K T                                       __________________________________________________________________________     33   1.12                                                                               1 1 0 0 0 2 1 2 0 0 0 1 0 0 0 0                                       33   4.48                                                                               1 1 1 0 0 2 2 3 1 2 1 2 0 0 0 0                                        35* 1.12                                                                               1 1 0 0 0 --                                                                               1 3 1 0 0 0 0 0 1 0                                        35* 4.48                                                                               1 1 0 0 1 1 1 3 2 3 1 1 0 0 1 0                                        38* 1.12                                                                               1 0 0 0 0 --                                                                               1 3 1 1 0 1 0 0 0 0                                        38* 4.48                                                                               1 1 0 0 1 1 1 3 3 1 1 1 0 1 1 0                                       41   1.12                                                                               1 1 0 0 0 1 1 1 1 2 --                                                                               1 0 0 0 0                                       41   4.48                                                                               1 1 1 0 2 1 1 1 1 2 --                                                                               2 0 0 1 1                                       66   1.12                                                                               0 0 0 0 0 2 2 2 2 4 0 1 0 0 0 0                                        80* 4.48                                                                               1 0 0 0 1 --                                                                               3 3 2 2 1 2 0 1 1 1                                       80   4.48                                                                               1 0 0 1 1 --                                                                               2 2 3 2 1 2 0 3 1 0                                       __________________________________________________________________________      *plants observed 2 weeks after treatment.                                

The above tables illustrate that the isothiazolecarboxylates and isoxazolecarboxylates of the foregoing formula (I) are effective in inhibiting the growth of undesirable plants. Especially preferred are those compounds in which X is trifluoromethyl in the 3-position and Y is either hydrogen or trifluoromethyl. Most preferred are those isothiazolecarboxylates in which X is trifluoromethyl in the 3-position.

The herbicidal activity of the isothiazole and isoxazole carboxylates of formula (I) is somewhat unexpected in view of the relatively weak herbicidal activity of corresponding isothiazolecarboxylic acid compounds, some of which are known compounds. Tables V and VI, below, summarize the results obtained when such isothiazolecarboxylic acids were tested in accordance with the heretofore described procedures. All observations were recorded 14 days after treatment. Table V summarizes the results of the pre-emergent test. Table VI summarizes the results of the post-emergent test.

                                      TABLE V                                      __________________________________________________________________________                 Rate                                                                               Plant Species                                                  Compound    (kg/h)                                                                             A B  C                                                                               D E F G H I J K                                          __________________________________________________________________________     3-(p-chlorophenyl)-                                                                        5.6 0 0 0 0 0 --                                                                               0 0 0 0 0                                          4-isothiazolecarboxylic                                                        acid                                                                           3-t-butyl-4-isothia-                                                                       5.6 0 0 0 0 0 0 0 0 0 0 0                                          zolecarboxylic acid                                                            3-phenyl-4-isothia-                                                                        5.6 --                                                                               0 0 1 2 --                                                                               0 3 0 0 1                                          zolecarboxylic acid                                                            3-(2,6-dichlorophenyl)-                                                                    11.2                                                                               0 0 0 0 0 --                                                                               0 0 0 0 0                                          isothiazolecarboxylic                                                          acid                                                                           __________________________________________________________________________

                                      TABLE VI                                     __________________________________________________________________________                 Rate                                                                               Plant Species                                                  Compound    (kg/h)                                                                             A B C D E F G H I J K                                          __________________________________________________________________________     3-(p-chlorophenyl)-                                                                        4.48                                                                               0 0 1 0 0 --                                                                               0 0 0 0 0                                          4-isothiazolecarboxylic                                                        acid                                                                           3-t-butyl-4-isothia-                                                                       4.48                                                                               0 0 0 0 0 0 0 0 0 0 0                                          zolecarboxylic acid                                                            3-phenyl-4-isothia-                                                                        4.48                                                                               2 0 1 2 0 --                                                                               0 0 0 0 0                                          zolecarboxylic acid                                                            3-(2,6-dichlorophenyl)-                                                                    11.2                                                                               1 0 --                                                                               0 0 --                                                                               0 0 0 0 0                                          isothiazolecarboxylic                                                          acid                                                                           __________________________________________________________________________

When operating in accordance with the present invention, effective amounts of the active ingredients are applied to the plant system. By application to the plant system is meant the application of the active ingredient in or on soil or plant growth media and/or applied above-ground portions of plants in any convenient fashion.

Application to the soil or growth media can be carried out by simply mixing with soil, by applying to the surface of the soil and thereafter dragging or discing into the soil to the desired depth, or by employing a liquid carrier to accomplish the penetration and impregnation. The application of liquid and particulate solid herbicidal formulations to the surface of soil or to above-ground portions of plants can be carried out by conventional methods, e.g. power dusters, boom and hand sprayers and spray dusters. The formulations can also be applied from airplanes as a dust or a spray because of their effectiveness at low dosages. in a further method, the distribution of the active ingredients in soil can be carried out by admixture with the water employed to irrigate the soil. In such procedures, the amount of water can be varied with the porosity and water holding capacity of the soil to obtain the desired depth of distribution of the active ingredients.

Tables I, II, III and IV indicate that the active ingredient is more effective when applied to the soil as a preemergent, i.e., before the weeds emerge from the soil, and this type of treatment is, therefore, preferred.

In selecting the appropriate time and rate of application of the active ingredient, it will be recognized that precise rates will also be dependent upon the desired response, mode of application, plant variety, soil conditions and various other factors known to those skilled in the art. While a rate of about 1.00 to 11.2 kilos per hectare is preferred, rates of from 0.05 to about 56 kilos per hectare may be used, depending upon the factors noted above. In addition, it will be recognized that single or multiple applications may be used to exert the desired response.

The active ingredient can be used alone or in combination with other pesticides or a material referred to in the art as an adjuvant in either liquid or solid form. To prepare such compositions, the active ingredient is admixed with an adjuvant including diluents, extenders, carriers and conditioning agents to provide compositions in the form of finely-divided particulate solids, granules, pellets, wettable powders, dusts, solutions and aqueous dispersions or emulsions. Thus, the active ingredient can be used with an adjuvant such as a finely-divided particulate solid, a solvent liquid of organic origin, water, a wetting agent, dispersing agent or emulsifying agent or any suitable combination of these.

Illustrative finely-divided solid carriers and extenders which are useful in plant growth regulating compositions of this invention include the talcs, clays, pumice, silica, diatomaceous earth, quartz, Fullers earth, sulfur, powdered cork, powdered wood, walnut flour, chalk, tobacco dust, charcoal and the like. Typical liquid diluents include Stoddard solvent, acetone, alcohols, glycols, ethyl acetate, benzene and the like. The compositions of this invention, particularly liquids and wettable powders, usually contain one or more surface-active agents in amounts sufficient to render a given composition readily dispersible in water or in oil. The term "surface-active agent" is understood to include wetting agents, dispersing agents, suspending agents and emulsifying agents. Such surface-active agents are well known and reference is made to U.S. Pat. No. 2,547,724, Columns 3 and 4, for detailed examples of the same.

Compositions of this invention generally contain from about 1 to 99 parts active ingredient, about 1 to 50 parts surface-active agent and about 4 to 94 parts solvents, all parts being by weight based on the total weight of the composition.

Although this invention has been described with respect to specific modifications, the details thereof are not to be construed as limitations, for it will be apparent that various equivalents, changes and modifications may be resorted to without departing from the spirit and scope thereof and it is understood that such equivalent embodiments are intended to be included herein. 

What is claimed is:
 1. A method for inhibiting the growth of undesirable plants which comprises applying to the plant system a herbicidally effective amount of a compound having the formula ##STR9## wherein X and Y are independently selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, trifluoromethyl, halogen, cyano and nitro; n is zero or one provided than when n is zero, Z is selected from the group consisting of chloro and NR₁ R₂ wherein R₁ and R₂ are independently selected from the group consisting of hydrogen and lower alkyl; when n is one, Z is selected from the group consisting of alkyl having up to 12 carbon atoms inclusive, haloalkyl, benzyl, lower alkoxy lower alkyl, allyl, monochlorinated allyl, dichlorinated allyl, ##STR10## and agriculturally acceptable cations; wherein R₁ and R₂ are as previously defined, R₃ is hydrogen or methyl and R₄ is lower alkyl.
 2. A method according to claim 1 wherein Z is alkyl having up to 12 carbon atoms inclusive.
 3. A method according to claim 1 wherein X is trifluoromethyl and Y is hydrogen or trifluoromethyl.
 4. A method according to claim 3 wherein X is in the 3-position.
 5. A method according to claim 4 wherein Y is hydrogen.
 6. A method according to claim 1 which comprises applying said compound to the soil before the emergence of the undesirable plants. 